GUNNERY
IN its early days this science might have been simply defined as the art of determining the motions of projectiles discharged from pieces of ordnance; in its present state it includes also the employment of projectiles specially adapted to the purpose in view, and the manipulation of artillery so as to enable the projectiles to produce the maximum effect.
Theory of Gunnery.— Instruments of great precision, mechanical construction of much accuracy, and a considerable knowledge of the higher mathematics are necessary to obtain and make use of trustworthy data for the establishment of sound principles on which to base the theory of gunnery. It is therefore not surprising that, owing to the early discovery of gunpowder, the art was long practised in a rude manner, without any attempt being made to reduce it to a science. Thus, though firearms appear to have been in use from the early part of the 14th century, little of value was understood of the laws regulating the flight of projectiles till the time of Nicholas Tartaglia, who published a treatise on the subject at Venice in 1537. About sixty years before that date, Leonardo da Vinci had enunciated some of the mathematical principles of trajectories in a manner which shows him to have possessed far more insight than any of his contemporaries; but he did not pursue the inquiry, and Tartaglia may be regarded as the father of ballistics. He was a man of great talent and ingenuity, but unfortunately had no opportunities of observing artillery practice; he was unable, therefore, to bring his calculations and speculations to the test of fact, and failed to carry conviction to the minds of the philosophers of the age. Before his time it had been generally believed that a ball on leaving the bore of a gun proceeded for some distance in a straight path,—a fallacy which lurks in the phrase “point-blank,” not yet expunged from popular speech. He saw, however, that “a piece of artillery cannot shoot one pace in a right line,” and propounded the axiom that “the more swifter a pellet doth flie, the lesse crooked is his range,”—a truth expressed at the present day by the statement that a high velocity gives a flat trajectory. This eminent philosopher claimed the invention of the gunner’s quadrant; he took into account in his calculations the resistance of the air, but placed the angle of elevation at which the maximum range would be obtained at 45°, which would only be the case in vacuo. Galileo was the next mathematician of note who investigated the subject. In his Dialogues on Motion, published in 1638, he recognized fully the resistance of the air, and pushed on the inquiry in the direction indicated by Tartaglia. It was not, however, till Newton’s time that a substantial basis was laid down for a true theory of gunnery. The grand discovery of the law of gravitation revealed the hitherto unguessed secret of the projectile’s fall to earth. The great improvements in mathematical methods of analysis invented by him rendered possible solutions of previously impracticable problems; while the splendour of his achievements in natural science stimulated philosophers of all countries. Towards the end of the 17th century he investigated the trajectory of a projectile on the supposition that the resistance of the air varied as the first power of the velocity. Bernoulli in 1718 gave a solution of the problem, on the supposition that the resistance varied as any given power of the velocity. This solution was, however, left in such a complicated state that no practical use can be made of it. No further progress was made till Benjamin Robins in 1742 published his Hew Principles of Gunnery, in which he furnishes a notable example of the manner in which theory should be wedded to practice, and hypothesis to experiment. Had Robins been in the possession of accurate instruments he would probably have arrived at results of considerable correctness. He invented the ballistic pendulum, and was the first to ascertain experimentally with any degree of correctness the velocities of projectiles on leaving a gun. A “triangle” or gyn supported a pendulum of iron having a massive wooden bob; to the bob was fixed a steel ribbon which passed through a steel clamp set to the desired pressure. A bullet fired into the wooden bob caused the pendulum to swing; the length of the arc described was recorded by the steel ribbon; the weight of the bullet and the conditions of oscillation of the pendulum being known, the velocity of the bullet could be calculated from the length of the arc. The weight of Robins’s first pendulum was 56 B), and it was therefore only suited for small arms. It could measure the velocity at only one point each round, and therefore, to ascertain the velocity lost by a ball in passing through the air, it was necessary to fire a series of rounds at one distance, and afterwards a similar series of rounds at another distance, Velocities of 1700 feet per second were measured, and the loss of velocity due to the resistance of the air, up to a distance of 250 feet from the muzzle, was approximately ascertained. Robins discovered that the resistance of the air was greatly increased as soon as the ball travelled faster than sound, and attributed it to the creation of a vacuum behind the shot, into which the air could not rush with speed greater than that of sound. Count Rumford in 1751 made use of the recoil to measure the velocities of bullets, on the principle that the momentum of the bullet forward was equal to the momentum of the gun backward. To carry this out, the gun was suspended as a pendulum, and the length of the arc it described on firing measured. By firing a bullet from a gun thus suspended into the ballistic pendulum, two independent records were obtained, and it would have been easy to calculate the lυs3 of velocity, from the muzzle to any range at which the pendulum could be hit, by the combination. The roughness of the methods unfortunately did not permit completely satisfactory results. Dr Hutton next took up the inquiry, and increased the weight of the pendulum and the bullets. No very great advance, however, seems to have been made till 1840, when experiments on the resistance of the air to the motion of spherical shot were carried on at ^Metz by the French Government. MM. Piobert, Morin, and Didion were the chief experimenters. They raised the weight of the receiving pendulum to nearly 6 tons, and fired into it 50-pound balls at a range of 330 feet. The information now obtained spread over a much wider field than that traversed by Robins. It was even found possible to construct the trajectories of projectiles with some approach to truth, and empirical formulae were laid down by which ranges and times of flight could be approximately calculated. It was not, however, till the introduction of electricity as a means of determining the velocities of projectiles that accurate knowledge of the resistance of the air was obtained. In 1840 Professor Wheatstone invented an instrument for this purpose, called the electromagnetic chronoscope. He has had many successors, whose productions exhibit a great amount of ingenuity; those from which the most valuable results have been obtained, and which are in use at the present moment, are the Bashforth chronograph, the Noble chronoscope, the Le Boulengé chronograph, and the Watkin chronograph.
The general principle on which these four instruments are designed is that a projectile after leaving the gun shall sever a fine wire stretched acros3 a screen, thus breaking an electric current, and causing a record to be made by the instrument at the moment. The Le Boulengé is connected with two wire screens only, the others with several. As two records are necessary to obtain a velocity, reading the time taken by the shot to pass between two screens, the number of points of a shot’s flight at which an instrument is capable of indicating the velocity is one less than the number of screens employed. The chronograph invented by the Rev. F. Bashforth, late professor of mathematics to the Advanced Class of the Royal Artillery, is shown in fig. 1.
A is a fly-wheal, which, in revolving, carries with it K, a cylinder covered with paper specially prepared to receive the records of the clock and screen. B is a toothed wheel which turns the drum M and unwinds the string CD, thus allowing the platform S to descend slowly down the slide L. E, E' are two electromagnets, whose keepers are supported by the frames d, d'; f,f are the ends of springs which act against the attraction of the electromagnets. There are two distinct currents—one through the screens and E, the other through the clock and E'. When these are interrupted, one by the shot cutting a screen, or the other by the clock beating seconds, so that the magnetism is destroyed, the spring/or/'carries back its keeper, which, by means of the arm a or α', gives a blow to the lever b or b', causing the marker m or m' to depart from the uniform spiral it has been describing—a spiral consisting of a double line running round the cylinder. The apparatuses adjusted so that the platform L, and consequently the markers rn, m', descend about ⅜ inch for each revolution of the cylinder; the folds of the spiral are thus I inch apart. The cylinder is made to revolve with considerable rapidity, so that the intervals between the successive clock marks indicating seconds measure from 20 to 25 inches; hence the screen marks indicating the moment of the severance of the wire by the shot can be allotted to their proper value in seconds with great accuracy. The screens are so contrived that the current, interrupted by the passage of the shot through one, is completed again before the next is reached. To accomplish this, the cutting of the wire is made to release a spring which makes a fresh contact; thus any number of screens can be used and a corresponding number of records obtained.
The chronoscope invented by Captain Noble of Elswick, late Royal Artillery (figs. 2, 3, 4), is constructed to furnish eight or more records, according to the number of discs, and is so excellently adapted for the measurement of exceedingly minute portions of time that it is usually employed to ascertain the velocity acquired by the shot in moving from a state of rest inside the gun at different parts of the bore. It is thus intimately connected with gunmaking, but, having the same character as other velocity instrument's, is described here. The screens used for recording the flight of the shot through the air are now discarded, and the
“cutting plugs,” shown in figs. 5, 6, 7, are substituted for them. In figs. 5 and 6 B is the bore, and A a flat-headed shot or cylinder passing along it in the* direction of the arrow. The plugs are screwed into the sides of the gun, as in fig. 7, which gives an end view of the bore. As
; the shot passes, its foremost edge pushes up the knife D, cutting the wire e, which passes in at one side of the plug C, then through a hole in the knife D, and out again at the other side of the plug. The ends of this wire are connected with the main wires leading to the instrument, and the knife D, in cutting it, interrupts the current. Fig. 4 shows a 10-inch gun pierced to receive cutting plugs in eighteen places. The main wires run from a plug to the primary of a Ruhmkorff coil, fig. ∙2, near the instrument, with which the secondary communicates. Figs. 2 and 3 show the instrument in plan and elevation.
A, A are disks, 36 inches in circumference, fixed on a horizontal shaft S. This shaft is caused to rotate, so that the edge of the disks travel at about 1100 inches per second, by a series of toothed wheels F, F, gearing as shown, and worked into rapid motion by the handle C. This motion is kept up with regularity by the descent of the weight B acting on the hindmost shaft, the speed of which is multiplied 200 times at the shaft S. At V is a vernier, reading a graduated circle, which is fixed on the shaft S. The edges of the disks are covered with a coating of lampblack. One of the secondary wires G is brought from the coil, and placed in communication with the revolving disk; the other secondary wire H is fixed in a discharger Y, just clear of the edge of the disk. A stop-clock is placed on a stand D, and records the rate of revolution of one of the shafts. When the gun is fired the shot begins to move, and, as it travels along the bore, cuts the wires of the plugs in succession, breaking the primary currents, and causing sparks to pass in the secondary current from the dischargers Y, Y, to the disks A, A, which are in rapid revolution. The sparks burn off the lampblack and record their positions on the disks by a minute spot. Now if the shot could cut all the plug-wires simultaneously, all the spots on the disks would be in a straight line, but it does not do so, and during the intervals between the cutting of successive plug-wires the disks continue to rotate, so that the line of spots forms a spiral round the cylinder represented by the disks, as is apparent on bringing the machine to rest. The shaft S is then turned so as to place each spot in succession opposite an index, and the spaces travelled by the circumferences of the disks between the spots are read off on the graduated circle. As the circumference of the disks is made to travel at the rate of 1100 inches per second, and the vernier reads to thousandths of an inch, the machine indicates portions of time rather less than a millionth of a second; it is, in fact, practically correct to hundred-thousandths of a second. A millionth is about the same fractiou of a second as a second is of a fortnight. Thus the distance between two successi ze spots gives the actual time occupied by the shot in moving over the portion of the bore between two corresponding successive plugs, and therefore the velocity acquired at some point of this travel. As the increment of velocity is constantly decreasing after the charge is fairly lighted, the point at which the measured velocity is acquired is very slightly behind the middle of the space between the two plugs. The observations are worked out, accidental errors eliminated, and the results put in the form shown in column 3 of Table I.
The “crusher gauge” (fig. 8) is so closely associated in its use with the Noble chronoscope that it is convenient· to give a description of it here, though its indications are valuable to the gunmaker rather than to the gunner. In fig. 4 are shown three plugs, A, B, and C, driven through the walls of the gun, and terminating flush with the bore. These plugs contain gauges for measuring directly the pressure of the gas on the surface of the bore. They are of the same diameter as the cutting plugs, and can be used in any of the twenty-one holes pierced in the gun. Fig. 8 shows the construction. The bottom of the plug is chambered out, and a steel anvil E is placed at the top of the chamber. Against’ this anvil is pressed a cylinder of pure copper A, carefully tested for quality, which is held in its place by a spring B. A piston C fits accurately the lower part of the chamber, any ingress of gas being prevented by the gas-check D, which is flush with the bore. When the gun is fired the powder-gas presses the piston hard against the copper cylinder A, which yields and becomes shorter, expanding laterally. The plug is then removed from the gun, and the nozzle unscrewed; the cylinder is extracted and measured. Its compression is compared with those given in a table constructed from experiment, and the pressure of the gas per square inch recorded. With the chronoscope the velocities are obtained directly from the time shown by the instrument to have been taken by the shot in passing over the interval between two cutter plugs. From these velocities calculation deduces the pressures required to produce the increments of velocity. These calculated pressures are compared with and confirmed by those obtained directly from the indications of the crusher gauge. Table I. shows the nature of the information obtained from Table I. [table]
the combination of the two instruments, when used with a 38-ton gun, firing an 800-K> projectile, with 130 lb of 1 ’ 5-inch cubical powder.
The last velocity is calculated from that taken by a Le Boulengé instrument outside the gun. This chronograph, the invention of an officer of the Belgian artillery, is shown in figs. 9, 10, and its mode of application in fig. 11.
The shot, after leaving the gun, cuts the wire of the first screen, and subsequently the wire of the second screen. The wire of the first screen conveys a current through an electromagnet A (figs. 9, 10), which then supports a cylindrical rod C. This rod is sheathed with a zinc tube D, which is renewed from time to time as required; several short zinc tubes are slipped on, instead of one long one, if no great variation in the velocities is expected, so as to save material. Directly the first screen is cut, the rod C, which is called the chronometer, drops. The wire of the second screen conveys a current through another electromagnet B, which supports a much shorter rod F, called the registrar. The shot, in cutting the second screen, releases this short rod, which falls on a disk 0, setting free a spring Μ. This spring carries a horizontal knife N, which flies forward and nicks the zinc tube covering the long rod. The nick made by the knife, if released while the long rod is still suspended, is the zero point. The currents from both screens pass through a disjunctor by which they can be cut simul taneously. When this is done the long and the short rods fall at the same moment. A certain time is consumed by the short rod in reaching the disk, setting free the spring, and cutting a nick on the zinc. During this time the long rod is falling into a recess in the stand, deep enough to receive its full length. The instrument is so adjusted that the nick thus made is 4 - 435 inches above the zero point, corresponding to0∙15sec. This is the disjunctor reading, and requires to be frequently corrected during experiments unless the weather is exceptionally favourable to the electrical conditions. Instead now of using the disjunctor to cut both currents simultaneously, suppose the shot to cut them in succession; then the long rod will be falling for a certain time, while the shot is travelling from one screen to the other, before the short rod is released. The longer the shot takes to travel this distance, the farther the long rod falls, and the higher up on it will be the nick made by the knife. A simple calculation connects the distance fallen through by the rod with the time occupied by the shot in travelling over the distance between the screens, and hence its velocity at the middle point is known. A graduated rule is generally supplied with each instrument, arranged for a certain distance between the screens; from this any velocity obtained can be read off at once.
The electric chronograph, invented by Captain Watkin, R.A. is shown in figs. 12, 13, 14.
Two brass cylinders A, A revolve on pivots B, B, C, C. Between them, at the top, hangs a brass weight (fig. 13), suspended freely by means of a piece of steel B, which pivots in another piece A let into the base of the weight. Two arms E enter, on falling, two V springs on the bed of the instrument, which catch the weight, A finely-pointed brass wire, CD, enclosed through part of its length in an ebonite tube, passes through the upper end of the weight from side to side; the piece B of the weight is placed between the ends A, C of the lever arms of the holder (fig. 14). The arm CD pivots on the pin F; AB is fixed. K, K is an electromagnet; on its keeper H is fixed a strong spring· G, G. When this spring is placed between the ends B, D of the arms, it forces the opposite end C to press against A and to sustain the weight by gripping the piece B (fig. 13) of the weight. In this position the keeper H is at a short distance from the poles of the electromagnet. Directly the current is allowed to circulate, the keeper is attracted down to the magnet, the spring G, G is pulled away, a small spring L presses on the arm CD, the jaw AC flies open and the weight is released. The two cylinders A, A (fig. 12) form part of the circuit of a secondary induction coil. The screens are similar to those employed for the Bashforth chronograph; they are traversed successively by the shot, which momentarily interrupts the primary current, and thus causes an induced current to pass through the cylinders A, A. As these, however, are not in electrical connexion, the current has to pass across through the brass wire of the weight, which is in the act of falling. The cylinders are covered with smoked paper, and the passages of the spark in and out leave minute spots showing the exact position of the weight at the moment: any number of screens may be used, and a duplicate record is obtained in one experiment of the space fallen through by the weight, while the shot is traversing each interval between the screens. As before, a simple calculation connects time and space, and an ingenious scale enables the experimenter to read off the velocities whatever be the distance between the screens.
In all these instruments slight errors exist, arising from mechanical imperfection, or from irregularity in the electric currents; still, the accuracy arrived at is sufficient for practical purposes, as is well shown by the following table :—
Table II.— Velocities of Martini-Henry Bullets fired with two different Charges, observed with several Instruments. [table]
These instruments enable the experimenter to ascertain the velocity of a projectile up to considerable distances from the gun. With rifled ordnance no difficulty is found in hitting screens of moderate size at a range of 2000 yards; and, practically, the loss of velocity due to the resistance of the air can be determined for all ranges and all velocities.
It might be supposed that, having the means of acquiring this knowledge, the artillerist would find little difficulty in solving the grand problem of his art, which may be thus briefly stated :—Given a projectile of known weight and dimensions, starting with a known velocity at a known angle of elevation in a calm atmosphere of approximately known density; to find its range and time of flight, its velocity, direction, and position at any moment,—or, in other words, to construct its trajectory. This state of perfection has, however, not yet been reached; mathematics has hitherto proved unable to furnish complete formulae satisfying the conditions. The resistance of the air to slow movements of, say, 10 feet per second seems to vary with the first power of the velocity. Above this the ratio increases, and, as in the case of the wind, is usually reckoned to vary with the square of the velocity; beyond this it increases still farther, till at 1200 feet per second the resistance is found to vary as the cube of the velocity. The ratio of increase after this point is passed is supposed to diminish again; but thoroughly satisfactory data for its determination do not exist. From this it would appear that, as the motion of the shot increases in rapidity, the air finds continually greater difficulty in filling up the space left by the advancing projectile, but that, when once a point is reached where the vacuum in rear is complete, further increase of speed only encounters additional difficulty in displacing the air in front. The difficulty of meeting the conditions by mathematical formulae is very great, since the velocity of the projectile changes continually, and moreover is resisted by air continually varying in density as the shot rises and falls again. It is evident’that the greater the weight of a shot in proportion to the column cf air displaced by it, i.e., to the square of its diameter, the less effect will the resistance of the atmosphere have upon its motion; thus very heavy projectiles moving with very low velocities will be but little retarded by this cause. It is desirable, therefore, before proceeding to explain what has been done towards the complete solution of the problem above stated, to establish the limit, and investigate the trajectory when the resistance of the air is neglected.
Let v≈ muzzle velocity of projectile; e = angle of elevation; t=time of flight.
Let the projectile start with velocity v from the point O (fig. 15) in the direction OM, so that MOX is the angle of elevation. Let OM be the distance which would be traversed in a period of time t, if gravity did not act. Draw ON vertically downwards, equal to the. distance through which the shot would fall in time ( under the action of gravity only. Complete the parallelogram 0MPN. Then P will be the position of the projectile at the end of the time t. We have then—
OM=⅛ and ON = MP = ⅛y< 2 .
Therefore OM 2 = -MP.
ff
Since OM 2 bears a constant ratio to MP, the trajectory is a parabola, having its axis vertical, and OM for a tangent.
Again, the horizontal velocity ≈υ cose, and remains uniform; the initial vertical velocity =v sine, and is acted against by gravity. Then—
tr=OQ = t√ cos e 2∕=PQ = -γZ sin e-⅜yf 2 .
Eliminating t, we get—
y=x tan e - —-—- ,
2√ 2 cos 2 ∈
which is the equation to the trajectory, and is a parabola. To find the range, put y = Q ; the two resulting values of x give the position ηf~ sin 2β of the gun, and the end of the range, thus, OR= - .
In Robins’ experiments in 1742 and subsequent years, it became apparent that up to a certain point the resistance of the air increased with an increasing power of the velocity. Hutton in 1790 placed this point at 1600 f. s., and considered that the ratio decreased after this velocity was passed. He proposed as a formula for the resistance Roc av+lnfi. General Didion, in 1840, deduced from the experiments at Metz the formula Roc αv 2 ⅛δΛ The experiments with rifled projectiles carried on at Gavre in 1861 led Professor Hélie to the conclusion that the resistance of the air at practical velocities was more nearly proportional to the cube of the velocity than to any other working expression. He constructed a formula for the trajectory by empirically modifying the formula given above for the path of a projectile in vacuo thus—
ffiκ 2 ( 1 t kx ∖ u=x tan e - ——— 5 - - 5 + —; y 2 cos 2 ∈∖r 2 υ J from which he deduces an expression for the range which at low elevations for velocities between 800 f. s. and 1400 f. s. is very fairly accurate, and which furnishes the simplest method yet devised of roughly constructing a range table :—
where r=range in feet; V= velocity in feet per second;
E = angle of elevation; n·2
⅛=0’0000000458 —; w
<?=diameter of projectile in inches; w= weight of projectile in pounds; <7 = acc. of gravity=32’19.
The above value of h is given for ogival heads; with hemispherical, pointed, or flat heads a different coefficient of resistance would be required. The ogival is the form which suffers least retardation from the air. The most complete and valuable series of experiments yet carried out is that of Professor Bashforth (1865 to 1870) at Woolwich and Shoeburyness. He found that, velocities and forms being equal and similar, the resistance varies exactly as the square of the diameter of the projectile. He further arrived at the conβlusion that between 900 and 1100 f. s. Roc ⅛ 2 , between 1100 and 1350 f. s. Roc v 3 , and above 1350 f. s. Roc v i . These results confirm in great measure those previously obtained, but unfortunately do not lend themselves readily to the construction of mathematical formulae. Bashforth adopted the cubic law as his basis, as it offers the least difficulty in manipulation, and, putting R = cv 3 , made the coefficient c a variable, the values of which he has tabulated. His method consists in building up the arc of the trajectory bit by bit, taking each portion so that a mean value of c for that portion may be used without important error. The path of the projectile may thus be constructed with almost any desired amount of accuracy, but the process is excessively laborious, and requires the use of a lengthy set of tables which cannot be reproduced here. For a complete knowledge of the subject the reader is referred to Mr Bashforth’s work. Mr Bashforth, however, tabulated the loss of velocity due to the resistance of the air with regard to the time and distance of the shot’s flight, and subsequent experiments carried out by the War Office in 1878- 79 have now confirmed and extended the results he had previously obtained. As most of the problems of modern gunnery can be approximately solved by the use of these tables, we give in Table III. an abstract with explanation.
Table III.— Loss of Velocity of a Projectile in Times and Distances. [table]
The rate of loss of velocity is here inversely recorded for an ogival projectile having a weight in pounds equal to the square of its diameter in inches. Thue a 9-pounder shell of 3-inch calibre starting with a velocity of 2500 f. s. would retain a velocity of 400 f. s. at a distance of (26,696-5000=) 21,696 feet after a time of (34’166 - 5’000 = ) 29 Ί66 seconds. As the value of decreases the resistance of the air retards the projectile less; thus if the 3-inch shell weigh 18 lb it will overcome the resistance twice as well as the 9-pounder, since its — =0 ’ 5 instead of l ’ 0.
Example 1.—The 80-ton gun fires at a vessel in motion at a range of 2000 yards. The muzzle velocity is 1580 f. s., the calibre 16 inches, and the weight of projectile 1700 lb. Required the velocity on impact, and the time of flight.
Here d -=-⅛‰ = 0’1506
w Î70Ô 0’1506x6000 ft. =903 ft.
Selecting the m. v. 1580 f. s. in the first column, the second column shows 23,519 ft. Subtracting, 23,519 - 903 = 22,616. Running up the second column and using proportional parts, this number corresponds to a velocity of 1383 f. s., which is the velocity on impact, showing the projectile to have lost 197 f. s. of its velocity during flight. In the third column, opposite 22,616 feet, we find 31'929 seconds. Subtracting this from the time opposite 1580 d 2 feet, and dividing by —, we have i=— 1 - (32 544- 31∙929) 0∙1506 κ
= 4 - 084 seconds.
Example 2.—An observer in an earthwork notes the flash of a hostile gun; in 3} seconds the shell (blind) buries itself in the parapet, followed in half a second by the report of the gun. The shell is dug out, and found to weigh 60 lb, and to measure 15 centimetres in diameter. Required the range, the muzzle velocity, and the striking velocity.
The rango is here given by the velôcity of sound, which travels through air at an average rate of 1140 feet per second; so that r=3∙75× 1140 = 4275 ft.; d 2 - (15 cm.) 2 , (5∙91 ins.) 2 _ 0 . 5gt>1 . w 60 60 ’
r—=2488 ft., and i-- = 1'892 sec.
w w
We have now to consider what muzzle velocity will cause the projectile to traverse the given distance in the given time. It must move at a mean speed of 1315 f. s. Assume the muzzle velocity to be 1600 f. s.; corresponding to this are found 23,607 feet and 32 - 599 seconds. Subtracting from these the reduced range and time, we have 21,119 feet and 3O - 7O7 seconds; if the velocity has been correctly assumed, it is clear that the range and the time of flight should result in the same terminal velocity. In the present instance, opposite 21,119 feet stands 1130 f. s., while opposite 30’707 seconds stands 1125 f. s. Thus it appears that the velocity has diminished more rapidly in the time travelled than in the distance travelled. This shows that it is assumed too high. Trying 1584 f. s., and proceeding as before, each column indicates 1120 f. s., which therefore is the terminal velocity, showing that the projectile has lost 464 f. s. of its speed during flight.
Drift.— Projectiles fired from rifled guns do not move in a vertical plane, but deviate to the right or to the left according to the direction of their rotation. All nations have adopted the right-handed twist, probably because it happened to be selected first. If the observer stands in rear of the piece and looks at the gun when fired, the projectile rotates in the same direction as the hands of a watch. It then steadily bears away to the right. The reason of this is not very clearly understood; in fact, two rival theories are put forward to account for it. If there were no resistance of the air, the path of the shot would be a parabola, and the axis of an elongated projectile would remain parallel to its original direction. The resistance offered by the air causes the axis to tend to assume a position tangential to the trajectory. On leaving the gun the projectile moves in the direction of its axis, which is also the direction of the axis of the gun. The action of gravity soon causes the path of the shot to make a small angle with the original direction of the axis; that is, the trajectory soon deviates from a straight line; the axis of the projectile is urged by the resistance of the air to accommodate itself to the new path, but as the path is constantly changing, the axis is always too late, since the rotation tends to preserve its parallelism. Thus there is always an angle—depending in amount on the velocities of rotation and translation, weight of shot, and density of the air—between the axis of the shot GB and the trajectory CD (fig. 16). Thus far both theories agree as to the facts, but they differ as to the deductions. The first view is that the resultant resistance of the air, which has the effect of a force in the direction DC, tends to turn the shot about an axis passing through G, and perpendicular to the plane containing BGD, so that if the shot had no rotation, it would turn end over end. But as it has a right-handed twist, this motion is combined with that which the resistance of the air tends to impart to the shot, and the point A is therefore slightly deflected to the right at first. Continuing the action, the axis GA describes a cone about CD, rotating in the same direction as the shot rotates about its own axis. The resultant of the air’s resistance tends to increase the angle BGD, therefore the shot will have a sinuous motion: but as the first deflexion is to the right, and afterwards the point is more to the right than to the left, the deviation will on the whole be to the right. The other view is that, as the axis of the shot is always directed a little above the trajectory, the resistance of the air meets the surface on the under side, on which therefore there is more pressure than on the upper side. The consequence of this is that the friction of the air with the rotating surface is greater below than above, and therefore causes the projectile to roll bodily to the right while travelling forward. The path thus curves away from the vertical plane, and the resistance of the air tends to cause the axis to lose its parallelism with that vertical plane, though it is, as before, too slow in altering its direction to become tangential to the curve described. Crucial experiments to set this point at rest are as yet wanting. The “drift” or “deflexion” is usually corrected in the British service by inclining the tangent sight. The result of this is that as the range increases, the higher the sight is raised, and the farther is the eye-notch to the left of the vertical plane containing the axis of the gun. In the German service the tangent sight is placed vertically in the gun, and the deflexion is allowed for by a graduated sliding leaf in the head. The same arrangement is used in those British guns, as the howitzers, which fire variable charges, as the slope of the tangent sight will accurately suit only one muzzle velocity.
To ascertain the correct slope, the actual deflexion is determined for each gun on the practice ground at various ranges with a vertical sight; then, in fig. 17, AD is the line of sight when the axis of the gun is horizontal. CD is the line of sight with a vertical tangent sight set at the angle of elevation ADC required for the range DF. Since the projectile deflects to the right, it is necessary that the line CD should point to E in order to hit F. This is accomplished by inclining the tangent sight AB, so that BC shall give the requisite allowance. The relation is thus established. By similar triangles, BC^EF. then BC —AC tan BAC, and CD —AC cosec ADC, so CD ï D
ft ∙⅛⅛B∙ r ' ,lli " g ftβ an ≡ le ado < thβ ele ∙ ration) —e, the angle BAC (the slope of the tangent sight) — 0, EF (the deflexion) ≈d, and DE (the range)=r, we have tan 0≈= i - cosec .·.
r
The action of the powder charge, the travel of the projectile along the bore, the rifling, and, speaking generally, what take3 place inside a gun when fired, are matters specially connected with the designing and manufacture of ordnance, and are therefore treated under Gunmaking. Projectiles.— The requirements of modern artillery have necessitated many complications in the preparation and use of projectiles, which now vary greatly in their nature and in the purposes for which they are employed. A general description of the several kinds supplied to European armies will be found under Ammunition, and but few remarks will be required to connect them with the guns for which they are intended. Smooth-bored ordnance use solid round shot and case, common shell, and diaphragm shrapnel shell. Solid shot are used against masonry, wooden shipping, and masses of men. They were at one time fired red hot at shipping. Roughly, the cube of the diameter in inches multiplied by 0 ’ 133 gives the weight of the shot in pounds. Case shot consist of iron balls packed in iron or tin cylindrical cases. They are effective up to about 350 yards against troops, boats, and rigging, and are especially suitable for flanking ditches. Common shell are completely filled with powder, and are burst in flight by time fuzes, or, on striking, by percussion fuzes. They are used against men in masses, buildings, works, and material generally. Diaphragm shrapnel shell contain a small bursting charge and a number of balls. They are fitted with a time fuze which explodes the charge when they near the object, so that the released bullets fly forward. They are very destructive against troops. In addition to the above projectiles, incendiary shells, called carcasses, filled with a violently burning composition, are thrown into villages and amongst shipping. Ground light balls cast among the enemy’s working parties at night disclose their position. Parachute light balls contain a parachute tightly folded up, and a cup of illumining composition; they are fired with a fuze timed to burst in the air, and they then remain suspended for a time, throwing a light down on the enemy’s working parties.
The great advantage of rifling was long recognized in small arms and sporting pieces before it was extended to ordnance. The first rifled arms threw bullets which, except for certain projections designed to fit the grooves of the barrel, were spherical. These guns surpassed smooth-bores in accuracy, but it was not till the introduction of elongated projectiles that a distinct gain in power was recognized. The gain in accuracy is due in great measure to the superior correctness with which the ball is centred in the bore by the action of the grooves, while the rotation imparted to it annuls or greatly lessens the disturbing effect of the pressure of the air on surface inequalities, or of variations in the position of the centre of gravity. An elongated shot is also enabled to travel point first, or nearly so, and as the resistance of the air depends upon the area of the transverse section, a far greater weight can be given to the long than to the round shot without increasing this resistance. Thus, in addition to greater accuracy, rifling confers a flatter trajectory and greater penetration. The elongated form permits a head of the best shape, an increase in the contents of the shell, and the use of fuzes which explode when the point strikes an object. The projectiles used with rifled guns are case shot, common shell, shrapnel shell, and Palliser shell. The case shot differ little from those made for smooth-bore ordnance. Common shell are generally from 2j to 3 calibres in length. They are designed to contain as much powder as possible, consistently with strength of wall to resist the shock of firing. Their effect is almost entirely due to explosion; velocity has little to do with it beyond conferring range and penetration. Common shells are generally fuzed with percussion fuzes. They are effective for breaching, for setting fire to buildings, against troops if not much scattered, and especially against wooden or thinly plated vessels. The introduction of ironclad ships is almost entirely due to the terribly destructive fire of shells. Shrapnel shell are filled with bullets, and have a bursting charge only sufficient to open the case and release the contents, which then fly forward with the velocity possessed by the projectile before breaking up. The bullets and fragments very speedily lose this velocity after separation. It is therefore most important to judge the range correctly and to form an accurate estimate of the practice, so that the result of each round may guide the aiming and timing of the next. When the shrapnel is burst in the air by a time fuze, it is exceedingly difficult to judge its precision by the puff of smoke. The splashes or puffs of dust of the bullets striking the ground should therefore be carefully looked for. When the shrapnel is burst on striking the ground by a percussion fuze, it is much easier to estimate the accuracy of the shooting, and it is common therefore to get the range by firing a round or two with percussion fuzes before setting the time fuzes. If the ground is hard and the distance of the enemy such that the shell strikes at but a small angle of descent, percussion fuzes generally burst the shrapnel better than time-fuzes, which, in their turn, have the advantage at long ranges and over soft ground. For field service time-fuzed shrapnel should be burst at from 50 to 100 yards in front of the object, and about 10 to 15 feet above the ground. The cone of dispersion of the bullets and fragments is considered to be so proportioned that the diameter at any point of the axis is one-third of the distance of that point from the burst or apex. To get satisfactory results from time fuzes it is necessary to have a gun which shoots with great regularity, a fuze composition which burns evenly, and an accurate mode of setting the fuze. Of late years improvements in powder and design of ordnance have rendered the velocities practically uniform. The fuze composition is somewhat liable to deterioration, but is tolerably satisfactory; and a new fuze auger has just been introduced which can be set to any desired degree of accuracy. As the power of shrapnell shell is entirely due to the velocity possessed by the bullets when freed from the envelope, it is of paramount importance in long-range firing that the shell should start with a high velocity and retain as much of it as possible. It is considered that with field guns the velocity of the projectile at the moment of bursting should not fall below 800 f. s., otherwise the contents will have a much diminished effect. The bullets themselves should retain a velocity of about 500 f. s. on striking to be thoroughly effective. With the more modern field guns the effective range of shrapnel extends up to about 3000 yards; with heavy guns to 4000 or even 5000 yards.
Palliser shells are made of a mixture of selected brands of iron, and are cast in moulds so constructed that the metal of the head is in contact with iron and that of the body with sand. The head is thus “chilled,” as the rapid carrying off of the heat by the iron mould causes the particles of the metal to dispose themselves rigidly, and confers intense hardness, which property is essential for the penetration of iron plates. The head is of the ogival shape, that being found most effective in combining strength with sharpness (fig. 18). It is a moot point whether projectiles of hardened steel are more effective than those of chilled iron against armour. Probably the steel can get through a greater thickness, but the damage done by the fragments of the Palliser after perforation is more serious. The cost of the steel shell is about five times that of the iron ones. The bodies are cast in sand, because extreme hardness is not there required, and a sounder casting is thus obtained. No fuzes are used with these shells; they are burst by the shock of impact on armour which explodes the powder charge. It is doubtful if they would explode on striking iron vessels not armour-plated, and they would fail to burst on striking wooden ships. They are effective in destroying masonry, and have been driven through great thicknesses of stone. They hold about a quarter as much powder as common shell of the same diameter. The greatest penetration of armour yet known was obtained by the 80-ton gun at Shoeburyness in 1877. The target consisted of four 8-inch wrought-iron plates, sandwiched with three 5-inch layers of teak, the whole put together with immense strength. The projectile perforated three plates and the teak, digging its nose about half-way into the last plate, which was much cracked and bulged. The 100-ton gun has perforated with ease 22 inches of solid wrought iron plate strongly backed, but failed to drive a hole through a similar target when the plate was of steel. Very recently extraordinary penetration has been obtained by a 6-inch 70-pounder made by Sir W. G. Armstrong & Co. Fired with a velocity of nearly 2000 f. s., this small projectile pierced about 11 inches of wrought iron. The subject of penetration is treated under Gunmaking.
A description of some of the fuzes and firing tubes used in gunnery will be found under Ammunition. The general principle guiding the selection of time or percussion fuzes is that when a shell is required to burst in the air a time fuze is employed, when on striking an object a percussion fuze is chosen. In muzzle-loading guns (not using gaschecks), time fuzes are ignited by the flash of discharge; otherwise the shock is taken advantage of to light the composition by exploding a detonator. Percussion fuzes are sometimes found to act too rapidly; where it is desired that penetration to a certain depth in earth or other material shall take place before explosion, it is found necessary to slow the fuze by interposing a small column of composition, burning for, say, a quarter of a second, between the detonator and the bursting charge. In firing a heavy shell with high velocity at a weak vessel, the resistance of the side is so slight that it may happen that the fuse either fails to act (the shell not being sufficiently retarded to set it in action), or explodes the shell after it has passed through both sides. To meet this case a specially sensitive and rapidly-acting fuze has been devised.
Guns were formerly primed with loose powder and fired by a match, next by common quill tubes filled with composition and ignited by a portfire, then by detonating tubes exploded by a hammer. Now friction tubes have superseded these methods for ordinary service. When it is desired to fire a gun from a distance, or to fire a number of guns absolutely at the same moment, Abel’s electric tubes are employed. In them two fine copper wires pass down through the head, insulated by gutta percha, except at the ends, which are separated by τ ⅛th of an inch of a composition of subphosphide and subsulphide of copper with chlorate of potash. The other ends of the wires are in contact with the copper lining of two holes in the head. The wires from the battery are placed in these holes; when the curtent passes, the composition is heated to ignition and explodes the tube.
Service of Ordnance.— The general principles guiding the employment and manipulation of artillery are applicable to the schemes of warfare of all civilized nations. Slight differences exist in calibres and weights; but it may be taken that the considerations which regulate the service of English guns have the same force elsewhere. The details of manufacture, the systems of loading, and the methods of rifling, are the chief points regarding which artillerists differ; these matters are treated under Gunmaking. Of two pieces constructed with equal skill to perform the same kind of work, the heavier will always be the more powerful. Thus weight is the chief controlling element in the employment of guns, though cost and convenience of manipulation have often to be taken into account. The artillery of the present day is the outcome of a long series of improvements, and the whole system of this important arm bears traces of frequent modification and continual compromise. The first introduction of firearms appears to have taken place in England in the reign of Edward III. On the Continent it was probably somewhat earlier, but the actual date and the circumstances attending their introduction are involved in obscurity. It is said that cannon were used in the English expedition against Scotland in 1327, and at the battle of Crécy in 1346. In 1360 there were four copper guns in the Tower. For about two centuries cannon continued to be manufactured of copper, brass, or bronze, good castings of which were made long before the art of smelting iron ores was perfected. In the early part of the 16th century guns were sometimes made of wrought iron plates put together longitudinally and hooped with wrought iron. In 1545 cast iron ordnance were manufactured in England, and supplanted pieces of all other materials for a time. The growing needs of warfare, however, soon demanded guns possessed of fair mobility to accompany armies in the field, and the cast iron pieces used being found excessively cumbrous, bronze was once again resorted to for field artillery. From about the middle of the 17th century till the introduction of rifled cannon, all the heavier natures of ordnance—fortress, siege, and ship guns—were made of cast iron; and all the lighter—field and boat guns—of bronze. In 1717 the bronze foundry was established at Woolwich, and most of the smooth-bored field pieces, howitzers, and mortars used in the service were made there. The heavy cast iron guns were supplied by contractors, and proved by Government officials. The long peace which succeeded the Napoleonic wars was highly unfavourable to the progress of gunnery, but a great development took place in the arts and sciences, so that, on the breaking out of the Crimean War, the latest discoveries in metallurgy and the excellence attained in machinery at once enabled inventors to make a great advance in artillery. At the transition period, a few wrought iron smooth-bores, throwing spherical shot of 150 and 100 B⅛, were manufactured to overcome the resistance of iron plates then recently introduced for armouring ships. These pieces were speedily discarded for rifled guns; and practically it may be said that the adoption of steel and wrought iron for guns coincided with the change from smooth-bores to rifles, both steps of progress being thoroughly established about 1860. In spite of the great superiority of the new ordnance, it cannot be said that the old pieces are yet superseded; vast numbers of them exist over all parts of the world, and often form the only defence. Even the fortifications in England are still largely armed with them on land fronts; and though they are gradually disappearing, they yet claim notice. Bronze guns are now obsolete in the British service. Figs. 19 to 24 show typical kinds of cast iron ordnance. Those denominated acccording to the weight of their projectile are made strong enough to fire solid shot or shell; those called by the diameter of the bore fire shell only. It must be remembered that, with spherical projectiles, the solid must be heavier than the hollow kinds, which need not be the case with rifled ordnance, as the projectile may be of any length. The guns are used for direct fire, the howitzers for curved fire, the mortars for vertical fire, i.e., they are set at 45° elevation, and the requisite range attained by varying the charge of powder, instead of firing at various degrees of elevation, as with guns and howitzers.
The old field smoothbores were fairly effective up to 1000 or 1200 yards, and so established a great superiority over the smooth-bored musket; but as soon as the rifled musket was generally adopted, an advance in artillery power became necessary if the arm was to retain its position in the scale of efficiency. After the Crimean War Napoleon III. rifled his bronze field guns on Treuille de Beaulieu’s system, and the new pieces exhibited great merit at Magenta and Solferino in 1859. England, and indeed every
European power, was busily engaged in experimenting during this period. The early Armstrong guns in England, Broadwell’s and Krupp’s in Prussia, and imitations of the French plan in other countries, speedily caused field artillery to regain its place in war. The northern kingdoms of Denmark and Norway and Sweden, favoured by specially good iron ores, and free from the immediate alarm of war, retained cast iron as the material for light ordnance. Prussia had already begun to use steel for smooth-bores, and naturally adhered to it for rifled guns, while the coil system brought forward by Armstrong was found cheap and enduring in England. The new Prussian guns were breechloaders, constructed on the double-wedge system; they proved unsatisfactory, and since the Franco-Prussian war of 1870-71 have been abandoned in favour of a single-wedge system of great neatness and efficiency. The Armstrong guns were also breech loaders, and when tested by land and sea, on actual service in China, New Zealand, and Japan, proved to be very powerful when compared with the old smooth-bores, but also exhibited many defects of construction. At this time no thoroughly successful breech-loader had been invented, and England reverted to muzzle-loading, while the Continental powers for the most part endeavoured to improve their methods of breech-loading. In 1872 the British wrought iron and steel muzzle-loading flpounder of 8 cwt. had been introduced into the service, and the 16-pounder of 12 cwt., of similar construction, was being brought forward. Against these guns the Prussian 6-cwt. field breech-loader had no chance. Its lightness was almost its only merit. Throwing common shell with percussion fuzes (which were useless on soft ground), having but a poor muzzle velocity, and suffering much from retardation by the air, its effect was feeble compared with that of the British 9-pounders, which threw with 200 f. s. more velocity a time-fuzed shrapnel of excellent construction, while the 16-pounder, though not equally fortunate with the 9-pounder in the arrangement of its projectile, yet by sheer power and weight of metal surpassed in deadly effect every field gun in existence. England’s field artillery was undoubtedly the most powerful known at that period. No one was more alive to this fact, or more dissatisfied with it, than the Germans. Their great gunmaker, Krupp, forthwith improved his breech-closing fittings, and instituted series upon series of experiments till he produced two guns —one for horse artillery, and one for field batteries, also horsed—which were an enormous advance on the weapons previously employed against the French. The lighter gun weighs 7 cwt,, and throws a shell of 11 B) weight, with a muzzle velocity of 1525 f. s.; the heavier weighs 9 cwt., and throws a shell of 17 ft> weight, with a muzzle velocity of 1460 f. s. These are figures indicating power not to be attained by the English 8-cwt. gun, or even the newer pattern of 6 cwt. throwing a 9 tt> shell with a muzzle velocity of 1380 f. s., and the 12-cwt. gun, throwing a 16 5) shell with a muzzle velocity of 1360 f. s, The immediate consequence of the introduction of these improved German pieces was the instituting of a series of experiments in England which resulted in the production of a muzzle-loading field gun, weighting 8 cwt., and throwing a 13-Bb projectile with a muzzle velocity of 1560 f. s. Shrapnel shell from this gun will retain velocity over 800 f. s. (the speed below which they cease to possess high efficiency) up to 3500 yards range. In this new gun advantage is taken of all the latest improvements, such as an enlarged powder chamber, increased length of bore, polygroove rifling, rotation by gascheck, and powder specially adapted to the piece. Although the introduction of this field gun once more places English light-artillery in the van, further progress is near. Sir W.
G. Armstrong <⅛ Co. are now (1879) experimenting with field guns, both muzzle and breech-loading, yielding velocities of 2000 f. s., and no doubt a fresh development of the new principles of air-spacing and chambering (already initiated in the Royal Gun Factories) is at hand (see Gunmaking). never earned adoption. Subsequently the breech-loaders have been gradually ousted by 25-pounder, 40-pounder, and 64- pounder muzzle-loaders, with 8-inch, 6 - 6-inch, and 6∙3-inch howitzers, new patterns of which latter pieces have just passed their early trials. The 64-pounders were introduced in 1864. For naval purposes the calibre was chosen so that
32-pounder round shot could be fired from it on emergency. The 40-pounders are stronger, and fire much heavier charges than their breech-loading congeners. The 25-pounder was introduced in 1874 to supersede the 20-pounder breechloader for light siege trains, and as a gun of position. Ever since 1853 experiments have been carried out by the Eng lish and other nations for the improvement of mortars and howitzers, first in a smooth-bored and then in a rifled state. These experiments are still in progress, and it cannot be said that the art of throwing heavy shell at high angles has as yet arrived at perfection. In 1872 short pieces throwing shells of 180 lb and 64 lb were adopted,
The history of the progress of siege guns would be in a great measure a repetition of that of the field artillery. Briefly, the smooth-bored siege train of cast-iron 18-pounders and 8-inch howitzers was replaced in 1859-63 by one composed of 20-pounders, 40-pounders (figs. 25-28), and 7-inch rifled breech-loading pieces, with certain howitzers which but recently longer and more powerful shell-guns have been tried, throwing heavier projectiles with greater accuracy. In these new pieces polygroove rifling with gas-check rotation affords a hope that the necessary precision may be attained.
The “converted guns” must not be passed over, since they are largely employed to arm our land fronts and to provide cheap and efficient pieces for practice by the reserve forces. When first elongated rifled projectiles were introduced, a great many methods of strengthening the old cast iron ordnance were proposed. The most satisfactory was that put forward by Palliser, and consisted of lining bored-out cast iron shells with wrought iron tubes. Some of the smaller men-of-war carry these pieces, but the great majority are used only for the secondary purposes above mentioned. The 32-pounders of 58 cwt., and the 8-inch shell-guns of 65 cwt., have thus become 64-pounders, and the 68-pounder of 95 cwt. has become an 80-pounder.
Important as are the land-service pieces of the army to England, yet, viewing her naval supremacy as one of the chief sources of her greatness, we must consider heavy ship and coast-defence ordnance to take the first place in modern gunnery. The contest between guns and armour has now continued with scarcely any intermission for upwards of twenty years, during which time the armour has increased in thickness from 4 to 24 inches, and the guns from 68- pounders to 2000-pounders; that is, from the most powerful of the old cast-iron smooth-bores to the 100-ton gun. The first armour-piercing rifled guns were the 7-inch Armstrong breech-loaders, but their supremacy was of short duration. They were the heaviest made on that system, and were speedily succeeded by far more powerful muzzle-loaders. In 1867 8-inch and 9-inch guns had already been introduced. The 9-inch Woolwich rifled gun of 12 tons was tried in competition with the xv-inch American smooth-bore, which weighed nearly half as much again, against armour. The British piece gained a decisive victory. In 1868 it was decided to introduce a 10-inch gun of the same character. Since that time progress has been continual, and the latest productions of the three great gunproducing establishments of the world are the 71-ton steel breech-loader, recently tested, of the German maker (Krupp), the 80-ton muzzle-loader of Woolwich, and the 100-ton muzzle-loader of the Elswick firm (Sir W. G. Armstrong & Co.).
Tables IV. and V. show all the principal rifled guns in the land and sea services of Great Britain. It has always been an object with the authorities to assimilate the guns of the two services as far as their respective requirements will permit, and so to avoid multiplication of stores at the numerous home and foreign stations where supplies are made; but still it will be observed that considerable differences exist, and, judging from the progress of events, it appears likely that these differences will increase, because, as the science of gunnery becomes developed, each new kind of gun is more exactly fitted to the performance of the special work for which it is intended, and therefore less suitable for other purposes.
Table IV.— Land Service Rifled Guns. [table]
1 Special projectiles for penetrating masonry.
Table V. — Sea Service Rifled Guns. [table]
Table IV. shows five distinct classes of rifled ordnance.
1. The heavy armour-piercing guns (figs. 29,30) are mounted round our coasts in casemates and barbette batteries. Their function is to protect the British shores from the attack of ironclad ships, wooden vessels, and boats. They are accordingly provided with Palliser projectiles, common shells, and a small proportion of shrapnel shell. In order to strike vessels steaming past at high speed, great accuracy, combined with rapidity of fire, is requisite. The guns are aimed either by eye or map, according to the nature of the coast. In the former case, the detachment commander estimates the range, gives the necessary elevation by means of the tangent sight, directs the line of fire according to his judgment, jumps down and gives the word to fire—allowing for the vessel’s motion and the time of the projectile’s flight. The map system has been recently perfected by Captain Watkin, R.A.
In it the whole navigable front commanded by the battery is plotted down in small squares numbered and lettered. Tables of the distances of the centres of these squares, the degree of training on the traversing arc required to lay the gun on the desired square, together with the actual elevation necessary to deposit the shot in that square, are constructed for each group of guns.
In fig. 31 F is a fort defending the channel; ABFC the line of shore; O the object to be hit, a vessel passing. A, B, and C are stations of observation. In a convenient spot the commanding officer of the artillery in the fort places the map, over which play two arms A'O', CO' kept constantly parallel to the two lines of sight AO, CO, by means of mechanism actuated by currents of electricity transmitted by a cable connecting A and A', C and O'. As A'C' represents, on the scale of the map, the distance AC, the junction O' represents on the same scale the position and distance of the object O. Tell-tales are distributed in the casemates, which constantly exhibit the number of the square over which the vessel is passing, showing the position of the ship, so that when the gun, or group of guns, are loaded, they can be either laid in the ordinary way, taking the range from the tables, or, if the object is invisible from the casemate, by trailing the gun round till the number of degrees indicated by the tell-tale agrees with the reading on the traversing arc, and giving elevation to suit the range. The arcs showing the direction of the guns are so arranged that guns trailed to any given number of degrees are parallel with each other. Supposing that from smoke or other cause the object cannot be distinguished from C, an observer is placed at B, and the arm is shifted from C' to B'. The practical working of the system is as follows. The commanding officer watches the course of a vessel as indicated to him by the arms on the map, the observers at A and C constantly following the centre of the object with their glasses. He telegraphs to the battery orders to load and lay, in accordance with the instructions given for each square of the map, and transmitted to the tell-tales. As the vessel passes over the square for which the guns are laid, the commanding officer can fire electrically the group of guns by pressing a key with his finger, or he may direct each detachment to keep up independent practice, laying in accordance with the indications sent by him through the tell-tale. The arrangements for exploding submarine mines or fixed torpedoes, where hostile vessels are passing close to them, are somewhat of the same character as those above described.
2. The land-front guns of fortresses shown in the table are intended to overpower and quell the fire of any pieces λvhich can be brought against them by a besieger. They are very largely supplemented in most fortified places by a number of the old smooth-bored guns and carronades, which are well adapted for the use of case shot at close quarters, for sweeping the glacis, and for the defence of ditches. The rifled guns throw common shell into the siege works, and where possible among the enemy’s material. They harass his working parties and reliefs with shrapnel, and endeavour to cut down his parapets and dismount his artillery by direct fire.
3. Siege-train guns accompany an army on a campaign where great mobility is not required, and where it is necessary to reduce fortified places. They should be the most powerful pieces which the means of transport will permit. In the more civilized parts of the world, where roads and cl imate are favourable, it is generally considered that about 70 cwt. is the heaviest w eight of piece that can be carried with an army. In less favourable countries it is frequently impossible to transport more than half that weight. The early rifled siege-train guns were grouped into two classes. A unit of the heavy train comprised— [table]
A unit of the light train comprised— [table]
Lately 8 ’ 0" howitzers of 70 cwt. and 6 ’ 6" howitzers of 35 cwt. have been introduced, but their allotment has not yet been settled. Siege guns are supplied with special shell, somewhat similar to Palliser projectiles, for penetrating masonry; also with common and shrapnel shell. The howitzers rarely use shrapnel shell. On first attacking a fortress at a long range, the duty of the guns is to cut down the defender’s parapets, dismount his artillery, dismantle his ramparts, and subdue his fire, so as to facilitate the con struction of batteries nearer the place. In the meanwhile the howitzers lob heavy shell into his works, and bombard the town, if necessary. As soon as practicable, breaching batteries are thrown up in such spots as may be found suitable for the attack of a weak point. It is rarely possible to breach by direct fire in the case of works of modern design. Here it is that curved fire is so effective, and here it is that the accuracy of rifled howitzers becomes so necessary. In order to make a practicable breach up which an assault can be delivered, the masonry at B (fig. 34), must be cut away, and owing to the height of the cover at A the fire must be curved to reach a point sufficiently low. Direct fire— tir à plein fouet, as the French express it—would strike too high up. Sometimes a work is so constructed that it is necessary to strike a point half-way down the masonry revetment to form a practicable breach. As it is desirable to strike with as much force as possible in breaching, it is evident that where the profile of the work requires the angle of descent of the shell to be considerable, it is necessary to select a spot for the battery at the longest range compatible with accuracy. For, given a certain angle of descent, the longer the trajectory {caet. par.) terminating in that angle, the greater will be the remaining velocity. Sometimes the guns of the siege train are employed with an army in the field to hold certain valuable ground against attack. They are then called guns of position, and are so placed as to command the approaches most effectively, and yet, if possible, to be dragged away at the last moment in case of retreat. They will usually fire shrapnel shell when thus employed.
4. The all-important qualities of field guns (figs. 35, 36, 37) are mobility and shrapnel-throwing power. They must be able to make long marches rapidly, to change position with celerity, to crush troops and the enemy’s artillery with accurate, well-sustained fire at high velocities, and to support rough usage without detriment to their efficiency. They are supplied with shrapnel and common shell, and case shot, of which shrapnel form by far the largest proportion.
5. The 'mountain-train guns are both 7-pounders; they fire the same shell, but the heavier one uses a 12-oz. cartridge, while 6 ounces is as much as can be fired from the lighter one. Both guns are intended for mule transport, one mule taking the gun, another the carriage, and a third the wheels, &c.; but at the Cape of Good Hope the heavier 7-pounder is mounted on a light high field-carriage for transport as well as for firing, while in Ashantee the lighter 7-pounders were dragged on a kind of sleigh. The lighter gun is tolerably effective for nearly a mile, and the heavier for about a mile and a half. Some jointed guns, proposed by an artillery officer, are now under trial. They are composed of two pieces screwed together, and, being carried separately, form a gun of about twice the weight of the ordinary mountain gun. Great increase of power is expected from this method of construction. Mountain guns are principally employed to throw time-fuzed shrapnel at troops, and percussion-fuzed common shell into hill works and woods occupied by the enemy.
In Table V. the principal sea-service rifled guns are shown. Three kind3 of work are performed by them, viz., to pierce ironclads and armoured forts, to attack unarmoured vessels, and to keep up a fire on troops on shore or on approaching boats. The heavy armour-piercing guns are well provided with common shell, as well as with chilled projectiles, so as to perform the first and second duties, but they have a very small proportion of shrapnel shell, which is intended to be used by them against troops or boats only on emergency. The 7-inch and 64-pounder guns are supposed to be quite sufficient in ordinary cases for the second and third duties, assisted in the third case by the smaller boat guns. All these are well furnished with common shell and shrapnel.
Gun Carriages.— The development which has taken place of late years in the power of artillery has necessitated corresponding changes in gun carriages. Formerly, every carriage was capable of travelling to some extent; even the heaviest guns were mounted on carriages fitted with trucks, which permitted motion on the ramparts or about a deck. Later on, sloping traversing platforms were introduced, up which the gun carriage recoiled on firing. Extra means of checking recoil became necessary as the power of the guns grew; compressors, or friction plates, were introduced, and are now only partially superseded by the hydraulic buffer. Mobility of carriage has almost entirely been given up, except for field and mountain artillery. The heavier siege guns travel on platform waggons, not on their firing carriages; and it is possible that the traversing platform and slide principle will extend yet further.
Tables IV. and V. show how the various pieces in the British service are mounted. Differences of detail exist, but the general system is the same for all European countries. Wrought iron is rapidly supplanting wood in the construction of carriages, and there are signs that it will in its turn be in great measure superseded by a mild steel. The subject of gun carriages is too long and too complicated to be treated in detail here, but, as guns are of no use without carriages from which to fire them, it is necessary to give some idea of the chief modes of mounting modern artillery. Figs. 38, 39 show the details of the 9-pounder rifled muzzle-loader carriage. It consists of three parts, the wheels, the axle, and the trail. The wheels have oaken spokes and ash felloes, the tire is of wrought iron, the nave and pipe box (which holds the end of the axletree arm) of a mixture of copper, tin, and zinc. The dish is considerable, amounting to 2 inches in the 5-foot wheel. There is little strut, so that the lowest spoke is nearly vertical, and the tire forms a frustum of a cone, instead of being a cylinder. The object of this form is to obtain lateral strength, especially in travelling on uneven ground. The axletree bed is of wrought iron, constituting, with the axle, a beam of box-girder section, the axletree forming the bottom. The trail consists of two side brackets, fixed by two transoms, two bolts, and the trail piece carrying the trail eye. The brackets are made of plate iron, riveted to a frame of angle iron. The axle carries two seats for gunners; into the trail are fitted the elevating screw and wheel, and the drag shoe with chain hangs below. Fig. 38 shows the gun and carriage in the firing position; when it is desired to move it to any distance exceeding a few yards, the point of the trail is raised, the limber is brought up, the trail eye is passed over the limber hook and keyed fast. The gun carriage and limber then form a four-wheeled vehicle, and travel as such. Figs. 40, 41 show the limber, which consists of wheels and axletree similar to those of the gun carriage, ammunition boxes, platform, and a pair of shafts. In the British service each gun carriage and limber are drawn by three or four pairs of horses, according to the nature of the piece. The driver of each pair mounts the near horse; the off wheel horse is between the shafts. In some countries pole draught is preferred.
Fig. 42 shows a 9-inch gun mounted on a wrought iron carriage and dwarf platform. This arrangement may be considered typical of all sliding carriages on traversing platforms. The direction of the gun is changed as required by training the platform to the right or left, the trucks working on the racers, front and rear, which are usually of wrought iron, laid concentrically on a bed of stone. The level of the traversing platform rises towards the rear, so as to assist in absorbing the work of recoil on firing, and to facilitate running forward again after loading. The recoil is also checked either by a system of friction plates, called a compressor,. or by an hydraulic buffer, placed parallel to and between the sides of the traversing platform, so that the carriage on recoil forces a piston into a cylinder containing oil, which escapes, through holes cut through the piston held, into the space round the piston rod; the size of the holes and the amount of the oil regulate the resistance offered to recoil, and enable the gunner to stop the piece at the proper place.
Several kinds of carriages on the “disappearing” principle have from time to time been put forward. In these the gun is exposed to the fire of the enemy only while being aimed and discharged; loading is performed under cover. The Moncrieff carriages are the most successful of this class. In them the force of recoil is stored up and employed to raise the gun from the loading to the firing position. Colonel Moncrieff applies his principle in two ways: the recoil either raises a counter-weight or forces a piston into a cylinder, compressing, by the aid of a fluid, air already much compressed. The counter-weight carriages are used to some extent in coast defence, and the hydro-pneumatic carriages are under trial for siege-train guns. Plate V. gives the details of the former. On a level traversing platform rolls a carriage or “elevator,” which places the gun in the required position either for loading or firing. The end of the elevator opposite to that which carries the gun is weighted, so that the recoil causes the elevator to roll to the rear and the gun to descend, at the same time raising the weight, which is retained in the upward position till released after loading, when its descent again raises the gun. Thus the elevator is a lever of the first order working on a shifting fulcrum, the curve (an involute) of the rolling surface being so adjusted that the resistance of the weight gradually increases as the gun recoils, and finally stops it smoothly and without violence. Conversely, by this form the gun is raised to the firing position gradually and without being jolted.
Hydraulic Gear for Guns.— As soon as the weights of ordnance increased so greatly that their service exceeded the power of manual labour, it became necessary to find some substitute. Steam power is always at hand in steam vessels, and it was quickly seen that it was best applied through the medium of water pressure. The simplicity and compactness of hydraulic machinery, the circumstance of its direct action rendering toothed gear unnecessary, and the perfect control it gives over the motion of heavy weights, especially adapt it for the purpose.
Plate VI. represents the mode in which the system is applied to the working of the 80-ton guns on board H.M.S. “Inflexible.” A circular turret contains two guns placed side by side, and strictly parallel as to line. The hydraulic pressure is conveyed through the trunk A by pipes to the presses in the turret. At B is a press for elevating the gun; this press also absorbs the force vertically given off during recoil on the elevating beam C. D is the gun-slide which carries the recoil press G for checking the recoil. This press is supplied with a tank T, up into which the water from the press G must escape through valves V loaded to the required pressure by springs. Έ is the gun run forward in the firing position; its trunnion S is fixed to the end of a piston rod, the head of which enters the press G; when the gun E is fired it recoils into the position F, shown by the dotted outline. The trunnion S forces the piston home into the cylinder G, driving the water up into the tank; the trunnion fittings run along the gun-slide horizontally, and the attachment or saddle below the gun runs up the elevating beam C, which is pivoted at the fixed point T, so as to depress the muzzle outside the port P of the turret PR. The gun is then in the loading position. In the meanwhile the turret has been caused to revolve ou the conical rollers H, H by hydraulic pressure till the muzzle of the gun is brought opposite the loading apparatus, which is securely housed below deck. The water power is taken down the ammunition hoist K, which raises a truck L, carrying a shell, on the top of which is laid a cartridge, to the loading position Μ. The sponge N, similarly worked by hydraulic pressure, serves as a rammer also. To perform the operation of loading, the sponge is forced home through the bore of the gun against the bottom, by contact with which a button on the head is pressed, setting free a rush of water; this thoroughly and visibly drenches the bore, and prevents the remotest possibility of a burning fragment remaining from the previous round; the sponge is then withdrawn, and the ammunition raised to M; the sponge now becomes a rammer, thrusts the cartridge into the muzzle of the gun, and is drawn back; the truck is raised still higher, the rammer then pushes the projectile into the muzzle, and rams home both cartridge and shell together; a wad previously placed on the head of the rammer is left behind, fast in the bore in front of the projectile, which is thus prevented from moving forward. An indicator on the rammer shows whether the charge is home. The press B is then put in action to lower the breech, raising the muzzle to the elevation required to suit the range of the object to be fired at; the gun is run forward to the firing position E, and the turret is revolved till the guns point at the object. The sighting is not on the guns, but on the turret; the captain of the battery looks through a hole in the roof R, behind the guns, and arrests the movement of the turret at the correct place, when the line between the sights, which is parallel to the axes of the guns, is directed to the object. The firing may be performed either in the usual way, or by electric tubes and wires from a distance.
Plate V., fig. 2, shows a 100-ton rifled muzzle-loading gun, mounted en barbette for coast defence, and adjusted for hydraulic loading. After being fired the gun is traversed round to the position A, where its muzzle is brought opposite the loading apparatus G, which is contained in a recess in the parapet D. An hydraulic hoist E raises the ammunition on a truck F to the muzzle; a similar apparatus is constructed on the right of the gun, which is traversed to either at pleasure. The carriage B slides on the platform C, which pivots on P, a trunk through which is introduced the hydraulic power for running the gun back and absorbing the recoil.
Many other applications of hydraulic power to gunnery besides those just described are due to Mr G. Rendel of the great Elswick firm. One of the most novel is that adopted in H.M.S. “Téméraire,” in which 25-ton guns are mounted on the disappearing principle in a turret having no roof and no ports; inside the turret is a turn-table carrying the gun by the trunnions on two arms, which are raised by hydraulic power, enabling the gun to fire en barbette over the wall of the turret. The recoil brings it down again, and it is placed opposite the loading gear by revolving the turn-table. The general principles are the same as those on which the .previously described systems are constructed.
Loading.— This article would be scarcely complete without a reference to the comparative advantages of the muzzle and breech-loading systems. Many have been much impressed with the great superiority of breech-loaders as small arms, whether for sporting or military purposes, and have concluded that the same superiority must extend to ordnance constructed on this plan. Others, having seen the difficulty of avoiding complication and accident to the parts in the early breech-loaders, have hastily condemned the whole system. The truth, as is often the case, lies between the two views, as will be seen from the following considerations. The chief p0int3 of excellence to be attained by a field gun are—(a) high ratio of power to weight; (δ) immunity from injury by its own fire; (c) immunity from injury by the enemy’s fire; (T) capability of supporting the accidents of service; (e) rapidity and facility of manipulation; (f) efficiency of projectile, (a.) The power of a gun is most conveniently measured by the energy (in foot tons) communicated to the projectile on leaving the muzzle. The following table shows how the latest English and German field guns compare together in this respect. The English guns are muzzle-loaders, the German ones breechloaders.
Table VI. [table]
The English 9 and 16-pounders at the time of their introduction were the most powerful field guns known, but were after a time beaten by the new German guns, which will in their turn be beaten by the new English piece, the first supply of which was lately issued. Recently a trial was carried out of two field guns made by Sir W. Armstrong & Co. They were precisely similar in all respects, except that one was a breech-, the other a muzzle-loader. No difference in their excellence could be detected. Thus it may be considered as certain that the power of a gun is in no way affected by the mere fact of its being a muzzle-loader or a breech-loader. Should, however, the adoption of one system favour an improved construction, or lend itself more readily than the other to the use of improved ammunition, this equality would disappear, and whichever system should gain a decided advantage in power, which cannot be obtained by its rival, must certainly prevail. It is almost impossible to overrate the importance of high velocity, combined, of course, with efficiency of projectile. In the field it enables the gunner to place the enemy under fire at long ranges, and so to force him to change his formations, and show his hand. It intensifies both the moral and physical effect of shell upon troops. It permits the guns to occupy good positions without the necessity of constant moving to get within range. In entrenchment firing it is, if possible, of still greater importance. Low velocity projectiles fired from field guns are almost harmless against earthworks. They have not sufficient bursting charge to do damage to the work by mere explosion, nor impetus enough to cut down the parapets; while the defenders hear the gun and crouch under cover as the shell comes. Thus it is not surprising that all our recent advances have been towards high velocities. Nothing has tended more to this end than the enlargement of the diameter of the powder chamber, which facilitates the profitable consumption of increased charges. This improvement is found to act differently on the two systems of loading. A chambered muzzle-loιder requires an expanding cartridge (in field guns); a chambered breech-loader requires a breech-closing apparatus of increased size and weight. Supposing a satisfactory expanding cartridge to be devised, the muzzle-loader gains in ratio of power to weight. If this be found impracticable, the breech-loader secures an important advantage iα this respect. Experiments are still in progress, and it would be premature to pronounce definitely in favour of either at present, especially as some fresh discovery or new explosive may at any moment confer preponderance on either system. (6.) In the Franco-German War of 1870, a large number of old pattern doublewedge breech-loaders became unserviceable by their own fire. This difficulty appears to have been quite overcome in the newer patterns of Krupp field guns by the adoption of the cylindro-prismatic wedge, with Broadwell ring and steel facing-plate. It would probably be incorrect to affirm that a breech-loader has quite as great immunity from injury by its own fire as a muzzle-loader, since no joint, however well contrived, can be as strong as the solid-ended steel tube forming the breech of the latter. But, putting mathematical certainty of security out of the question, it may now be accepted that practically field guns can be made as safe and enduring on one system as on the other, (c.) As regards immunity from injury by the enemy’s fire, the muzzle-loader has a decided advantage. It is difficult to estimate the real value of this advantage, depending as it does partly on the manner in which artillery is employed, and partly on the doctrine of chances. During the Russo-Turkish War of 1877-78 but few guns were placed hors de combat by the enemy’s fire. In such cases as did occur, the injuries were nearly always such as would not have effected muzzle-loaders. The wedge handles were usually bent up by the action of percussion fuze shell jamming the wedges. The Russian field guns were generally of a feeble class; the proportion of entrenchment fighting was unusually large; and in the field the Turkish artillery habitually fired at long ranges. It may therefore be fairly concluded that the number of guns injured by the enemy’s fire was not so great as to render the superior invulnerability of muzzle-loaders of much importance. These conditions will probably be reversed in any great war in which England may take part; and hence the advantage gained by muzzle-loaders in immunity from damage by hostile fire must be carefully borne in mind in comparing the two systems of loading, (cl.) In capability of supporting the accidents of service, there is not much to choose between the two rivals. The breech-loader is more liable to injury from being upset, and exposes more parts and finer fittings to the action of the weather. On the other hand, it is easier to clean, and the officer can better see that it is clean. The jamming of projectiles in the bore when ramming home, which sometimes occurs with muzzle-loaders, is impossible with breechloaders. This defect, it is hoped, has been overcome in the new English field gun. The preservation of breechloaders, especially in mountainous countries, necessitates a profuse expenditure of oil and grease, (e.) In comparing the rapidity and facility of manipulation of the two methods of loading, it is necessary to consider the circumstances under which the guns are employed. Suppose a horsed battery of guns to gallop to an open spot whence they command a body of hostile troops in motion. Coming into action, the gunners load and fire as rapidly as accuracy will permit, unhampered by parapets. It is evidently of great importance to throw as many projectiles as possible among the enemy. Here the muzzle-loader will have some advantage. With full detachments in the open it takes rather les3 time to load, aim, and fire a muzzle-loading field gun than a breech-loading one. The reason of this is that with the former the man laying the piece can manipulate the sight and usually take aim while the loading is being performed, while, when the projectile and cartridge are thrust in from behind, he has to wait till the loading is done before he can get to the sight. There is no practical difference in the time occupied by the actual loading. In one case, the cartridge and shell are rammed down a long distance together; in the other, first the shell is put in a short distance, and afterwards the cartridge, and the wedge has also to be withdrawn and replaced. Next, suppose a commanding position to have been selected for a battery, and a light entrenchment to have been thrown up, over which the guns fire. Here the muzzle-loader will lose the advantage gained when firing in the open, as it must be loaded before being run up to the parapet, and aimed afterwards. Both natures of gun recoil, and it makes no difference in time whether the ammunition be thrust home when the gun is back at the recoil position, or after it is run up. Here the breech-loader and the muzzle-loader stand upon equal terms. Thirdly, suppose—a rare case with field guns—that firing with reduced charges is required, that shell are being lobbed from behind a parapet at high angleβ into a work. Here we shall have little recoil, probably not enough to permit loading at the muzzle without the gun being run back by hand. Loading at the breech will, however, be perfectly simple. In this case the breech-loader gains a very decided advantage over the muzzle-loader, since not only does it not require to be run back, but it has to be run up merely a very short distance. To this the advocate of muzzle-loading will probably reply that shells are lobbed with low velocities into works only at considerable intervals of time, that rapidity is therefore of no use, and that the advantage claimed is worthless. No doubt there is truth in this argument, but suppose the action of reduced charges on the gun to be imitated by the introduction of a brake which shall check the recoil within a short space, even when the gun is firing rapidly with high velocity, then the breech-loader behind entrenchments gains a distinct advantage. The German guns are supplied with powerful but clumsy brakes, more for travelling purposes than for firing, and it is doubtful how far they answer for the latter object. In the British service it has not been thought important to check recoil, since a certain amount of it has been necessary for loading behind parapets; but trials have been made of brakes, &c., for the purpose of preventing guns from running backwards down a reverse slope when fired from the crest of a hill, or, more generally, for checking excessive recoil. Up to the present time (1879) no great success has attended these efforts, nor does it appear feasible to abolish recoil altogether by sinking the wheels in a ditch, since the strain on the carriage would then be much increased. There is no doubt the question offers grave difficulties, especially as lightness is such an important feature in the construction of field gun carriages. As yet, then, the reduction or checking of recoil behind a parapet confers but a problematical superiority on breech-loaders, and cannot be held to counterbalance the advantage gained by muzzle-loaders in the open, (fj) In the older pattern guns of both systems, where studs and windage were pitted against lead coating and no windage, the muzzle-loading projectile was able to take a better time-fuze than could be used in the breech-loader, but it did not possess the same accuracy of shooting. Since the introduction of the polygroove system, in which rotation is given and windage sealed by a copper-flanged ring or disc at the base of the shell, the muzzle-loading projectile ha3 lost the advantage of being able to use the simpler time-fuze, but has gained in several important respects. The breech-loading shell has also been improved by the substitution of two copper wires for the lead coating, but is probably inferior to the new muzzle-loading projectile, which, however, can be used equally well for breech-loaders. It may be said therefore that the systems are equal in respect to efficiency of projectile.
Thus then, taking the six qualities named as chief excellences to be sought for in field artillery, it appears that in four of them there is practically little or’ no advantage gained by either system over the other, while, in the two remaining qualities, the muzzle-loader has slightly the best of it. On the whole it seems therefore that, at the present moment, the balance of evidence is in favour of muzzle-loading for field guns.
In comparing the advantages of the rival methods of loading siege guns, the entirely different character of the two classes of pieces composing a train at once forces itself on the attention. One class consists of long guns, projecting far over a parapet, and usually fired at low elevations with heavy charges; the other of short guns, usually fired at high elevations with low charges, the muzzles on recoil coming well within the emplacement. The Germans use long and short 15-centimetre guns, both breech-loaders, and both throwing shell of the same weight. The long gun, fired with heavy charges, weighs three times as much as the short gun, which is fired with light charges. Supposing the dimensions of the short gun were increased, the proportions remaining unchanged, till its weight equalled, that of the long gun, then it would be able to fire shell of three times the weight. This is what is actually being done in the British service. Now all these heavy pieces, firing either heavy powder charges or heavy shell, require very strong and consequently very heavy carriages to bear the recoil, and it is found convenient to transport the guns on comparatively light platform waggons apart from their firing carriages. Hence there is no longer any necessity for constructing firing carriages with a view to travelling purposes; and it is probable that traversing slides will be introduced for all heavy siege pieces. It is not requisite to institute at length a comparison of the various qualities desired for siege guns. Rapidity is very rarely of importance with them; they are always fired under cover, and it may be at once assumed that, as far as power and endurance go, the two systems are practically equal. A fresh set of conditions comes into play: the projectiles are heavy; and convenience of loading, combined with safety to the gunners from the enemy’s fire, should now be considered. As these points are connected with the form of carriage employed, it was necessary to call to mind in comparing breech with muzzle loading, that slides are likely to take the place of travelling carriages. When long guns are fired, in order to permit loading at the muzzle, it is requisite that the recoil should be great, and the emplacement deep. Many devices, such as flexible rope rammers, jointed staves, &c., have been tried, but have not proved perfectly successful in overcoming this difficulty. Breech-loading here has a considerable advantage. Long guns are fired at low angles of elevation, and no difficulty therefore is experienced in thrusting the projectile home from behind in a nearly horizontal bore. High velocity is required, and the breech-loading system lends itself readily to enlargement of the powder chamber, without necessitating the complications of an expanding cartridge. If slides are used the hydraulic buffer checks the recoil at once; on the other hand, the parapet affords rather better protection to men standing close to it at the muzzle than to men standing a little way off at the breech. These conditions are reversed with the short pieces. The rammer is short, and no great recoil is necessary to permit loading at the muzzle. The elevation is high, and it is much easier to drop a shell in from the front than to thrust it up from behind. Indeed this cannot usually be done, and a breech-loader has to be brought nearly horizontal for loading. High velocity is never required, and enlargement of powder chamber is not wanted. The men are in the most sheltered position at the muzzle. If these views be admitted as correct, it seems clear that the long pieces of a siege train should be breech-loaders, and the short ones muzzle-loaders. To this it may be objected that uniformity would be sacrificed by such a combination. There is not much in this objection. The mere fact of two guns being loaded in different ways is surely of little consequence, and can easily be grasped by the dullest gunner. It is done every practice day on board ship, where the old pattern Armstrong vent-piece breech-loaders are combined with modern muzzle-loaders. As regards the stores, a long and a short gun of the same weight would not under any circumstances fire the same ammunition, and even in cases where a heavy long gun is associated with a light short one having the same diameter of bore, as in the case of the German 15-centimetre pieces, there is no reason why the same projectile should not be used for both if desired; that is, the new smooth muzzle-loading shell, with a gascheck on the base, would answer for both.
The question of breech-loading or muzzle-loading is obviously not only complicated, but is liable to alteration in its conditions with every advance made in the science of gunnery. To decide that an army or a navy should have nothing but breech-loaders, or nothing but muzzle loaders, would be to make a fetich of uniformity; there is plenty of room for both systems. With regard to heavy fortress and ship guns, it is easy to suggest positions where it will probably be found that one system has a decided advantage over the other. Thus, taking the sea service first, in turrets the muzzle-loader is preferable. The loading can be performed with great facility outside the ports, and a turret of a given diameter will house a pair of bigger guns than when the loading has to be done inside at the breech, unless some method of exterior loading can be devised for the breech-loaders also. For broadside guns, on the other hand, it seems equally clear that breech-loading has the advantage, as muzzle-loaders have to be run in so far to permit loading that they must be too short for ballistic excellence. For a small gun placed on a slide in the bow of a boat, it appears far more convenient to load at the breech. For those gunboats in which the vessel is simply the gun carriage and the line of fire is given by the helm, loading at the muzzle from below deck offers great advantages. Land service heavy guns, mounted on sea fronts for the protection of harbours, <fcc., present a great variety of conditions. In some cases the rocks or ground on which the battery is erected have such a form that a heavy gun loaded at the breech could be used where only a comparatively small one could be loaded at the muzzle. Sometimes a turret can be erected with loading gear outside, and then the conditions are reversed. In the case of very heavy guns, which once ⅛ situ are not intended ever to be moved, the argument from uniformity loses much of its cogency; and the circumstances of every gun position could therefore be separately considered. The guns and howitzers arming land fronts of fortresses should follow the same rule as given for the siege train, the conditions of service in battery being very similar. The long pieces should be breechloaders, the short ones muzzle-loaders. Wherever the comparative advantages of breech-loading and muzzle-loading are nearly equal, the decision should be in favour of the muzzle-loaders as possessing the inherent advantages of simplicity, solidity, and cheapness.
Conclusion.— The science of gunnery has received so many developments of late years, and is even now progressing so rapidly, that it is impossible to do justice to the subject within the limits of an article. The reader who wishes for more minute details, and who would study any part of the science thoroughly, is recommended to consult the following list of works :—
English. —Robins, New Principles of Gunnery ; Gen. Boxer, R.A., Treatise on Artillery·, Col. Owen, R.A., Modern Artillery; Majors Griffiths and Duncan, R.A., Artillerist’s Manual·, Major Sladen, R.A., Principles of Gunnery·, Rev. F. Bashforth, Motion of Projectiles ; W. D. Niven, On the Calculation of the Trajectories of Shot ; Capt. Noble and Prof. Abel, Researches on Explosives; W. W. Greener, Modern Breech-Loaders and Chokebore Guns; Proceedings of Royal Artillery Institution (quarterly); Lt.-Col. Strange, R. A., Manual of Field Artillery for Canada; Reports of Committee on Explosives; Reports of Committee on High-Angle Fire; Changes in Artillery Matériel and Stores ; and the War Office publications— Proceedings of Ordnance Select Committee; Text-Book on Ordnance; Text-Book on Ammunition; Text-Book on Carriages. French. —Gen. Didion, Traité de Balistique-, Id., Lois de la Resistance de l’Air; Prof. Hélie, Traité de Balistique Expérimentale ; G. Piobert, Traité d , Artillerie Théorique et Expérimentale; Revue d'Artillerie (monthly).
Italian. — Rivista Marittima (quarterly).
American. —Holley, Ordnance and Armor; Annual Reports of Chief of Ordnance. German.— Handbuchfur die Offiziere der Königlichen Preussischen Artillerie, Berlin, 1877; Mittheilungen über Gegenstände des Artillerie und Genic- Wesens, Vienna (monthly); Handbuch fur die K.K. Artillerie, Vienna (published in sections, 1871-77); Maj.-Gen. Count Bylandt-Rheidt, Der indirecte Schiess mit Hohlgeschossen, Vienna, 1874; Prof. Georg Kaiser, Theorie der Elasticität und Festigkeit röhrenförmiger Körper, Vienna, 1876; Id., Ueber Laffeten-Construction, 1877; Militär-Wochenblatt, Berlin.“ (E. Μ.)
Note.— The publishers are indebted to the kindness of H.M.’s Stationery Office and the Royal Artillery Institution for assistance in preparing some of the illustrations for the foregoing article, ·
