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Bible Encyclopedias
Trench Ordnance
1911 Encyclopedia Britannica
or "TRENCH ORDNANCE. - The need of some form of easily transportable weapon for bombarding an enemy's works or his men from trenches immediately facing them, instead of from a distant artillery position, has made itself felt throughout the history of siege warfare. The use, in the trenches, of small mortars (known as " cohorns," from the Dutch engineer Coehoorn who designed them) was habitual in the sieges of the 18th century, and the great Carnot early in the 19th century proposed their use on a very large scale for the purpose of attacking personnel protected from direct fire by breastworks. The introduction of rifled ordnance, and the consequent modifications in siege methods, led to the disappearance of these cohorns. Nevertheless the need of a trench-mortar was felt in both of the two great sieges of modern times - Vicksburg and Port Arthur - in which, before the World War, trench fighting was close and prolonged. In these cases mortars of wood and hoop-iron, strong enough to bear the strain of throwing small bombs a short distance, were improvised by the troops themselves. After the experience of Port Arthur, however, European designers took up the question, and several types were worked out, of which three, the Belgian Aasen, the German official " Military Engineering Committee's " design, and the Krupp, initiated progress along three different lines which were followed up in the World War. The first named, which was used in action even before the World War - at the siege of Adrianople, 1913 - was the prototype of the light trenchmortars; the second, with few important modifications, remained in service throughout the WorldWar, and represents the adapta tion of standard artillery ideas and elements to the new problem, while the third introduced the principle of the " stick-bomb," fired from a small-bore high-pressure cannon. The Aasen, besides opening the series of light trench-mortars, introduced the principle, opposite to that of the Krupp, of low pressure.
The history of trench-mortars in the World War is a record, first of a continually increasing demand which the supply authorities in the various belligerent countries could not meet; then of a period, coinciding with the full development of positionwarf are methods of tactics, in which well-designed weapons with ample ammunition supply played an increasingly important part; and lastly of a period in which, under pressure of new tactical needs, the " trench " mortar strives to become a gun of "accompaniment." The tactical employment of trench ordnance, whether in its designed role or as accompanying artillery, is dealt with under Artillery: the present article is concerned with the weapons themselves.
The German trench-mortars - handled not by artillerymen but by engineers in their capacity as the technicians of the siege trenches - were used with great effect in the attack of certain of the Liege forts, and a little later at Maubeuge and Antwerp. In this they were. carrying out the special duties for which they were designed, and at that stage of the war it was not foreseen that weapons of this class would be required for the equipment of a trench-front hundreds of miles in length. Consequently very few were available when the western front became stabilized, and the demand was made simultaneously from all quarters for some short-range trench weapon capable of curved fire, by which alone the covered enemy could be attacked from covered positions. For the time being, it was impossible for any belligerent to do more than provide stop-gaps in the form either of mechanical throwers (see Bombthrowers) or small mortars mounted on wooden beds, which were in fact either artillery shell sawn off at the neck and bored with a vent or else cohorn and other mortars of the smooth-bore era, unearthed from arsenals or museums. But while the troops made shift with these, inventors and de-, signers were producing experimental models which, when approved, were brought out in enormous numbers, with little difficulty from the point of view of manufacture since the designs were deliberately kept simple so as to be serviceable in the roughest conditions.
Setting aside, for the present, direct-fire trench-guns, of which various types came into use for combating machine-gun emplacements, and, later, tanks - trench ordnance for curved fire is classified either according to weight, as light, medium or heavy, or according to the principle of design, as high-pressure or low-pressure. The latter basis of classification is taken here; and it is desirable at once to indicate the specific differences which mark off trench ordnance from normal artillery weapons, applying equally to high-pressure and to low-pressure types.
The most important difference is in range. Although by the end of the World War some remarkable results had been obtained by progressive experiments in the direction of increased range, the trench-mortar remained essentially a weapon of less than 2,000 yd. effective range. In the earlier models - save a few - the limit was about Soo yd., while many were incapable of exceeding 250. Even this last range sufficed in some cases, owing to the short distances separating the opposed front lines, and during the period of position-warfare most of the work of light and medium trench-mortars was done at ranges of 400 to 600 yards. The main motive for increasing range was not the desire to reach a more distant target from the front line, but the desire to emplace the trench-mortar at such a distance behind one's own front-line troops that premature explosions - specially liable to occur with improvised ordnance and ammunition - would not affect them. An almost equally cogent motive was the desire to avoid drawing the enemy's reprisal-fire, time after time, upon the same body of friendly infantry. Another motive was the desirability of withdrawing the trench-mortar itself from the effects of fire directed upon the front line, and preventing too close observation of its position by the enemy.
The next point is weight. For use in or near the front trenches the trench-mortar must be portable, either as a single unit (as in the case of light mortars) or in parts which severally do not exceed certain limits fixed by experience, either in point of weight or in point of dimensions. For the heavier trench-mortars, having greater range, the limits imposed on those which have to be taken close up to the front line are somewhat relaxed; indeed, the very heaviest, used only in very favourable conditions, is designed for a concrete bed and light-railway transport.
A third point is simplicity, or better, in the French phrase, " rusticity." The trench-mortar is by hypothesis subjected to the worst conditions of exposure and handling. From birth it lacks the mechanical finish of standard artillery; it is required in great numbers at a time when all engineering shops for high class ordnance works are fully occupied and take the pick of the available metal. Then, on service, it is handled in the main by a hastily trained personnel, not all of whom possess the gunner's respect for his gun or the mechanic's pride in his machine. Moreover, the medium and heavy models are in most cases taken down and assembled frequently, and the parts are transported by hand through winding, muddy trenches, or across broken country in the dark. Save perhaps a detachable sight (which is carried by a non-commissioned officer or gunlayer), none of the customary adjuncts of modern ordnance is admissible.
Lastly, the ammunition, even of rifled trench-mortars, differs considerably from that of standard artillery. In most cases its design is special to the particular design of mortar, and there is no interchangeability such as that of 6-in. gun and howitzer ammunition. But in all cases, not being exposed to the bore pressures which standard artillery ammunition must endure, it has much thinner walls and a far greater explosive content.
These specific differences will be best realized by comparing a standard heavy trench-mortar with a heavy howitzer of the ordinary kind. The trench-mortar here taken is the Batignolle 24-mm. used by the French, British and Italian armies; the howitzer the German 21-cm., 1910 model, with a somewhat thickwalled shell.
| Shell | Weight g of gun exclu- sive of | Pro- pellant | Burst- ing | % of Burst- er to weight | Range ing | mount- ing | Charge | Charge | of filled shell | Metres | kgm. | kgm. | grm. | kgm. | % | Trench-mortar | 89 | 220 | 720 | 45 | 56 | 1,040 | Howitzer. . | 83 | 2,625 | 3,200 | 8 | 9.7 | 9,100 Here the trench-mortar shows roughly one-fifth the propellant charge and one-ninth the range, but one-twelfth the weight of gun and six times the shell " efficiency " of the howitzer. All trench-mortars fire at super-angles; that is, they use elevations of about 47° for their longest range and highest elevations up to 75° or more for the shorter ranges. This enables them to be used from deep and narrow trenches. The design may now be considered under the three headings of high-pressure smooth-bore, low-pressure smooth-bore, and rifled. IHigh-Pressure Smooth-Bore Trench-Mortars. The prototype is the Krupp bomb-gun of 1912. This, and all the types presently to be described have " stick-bombs." The stick-bomb is a large-bodied explosive container sometimes spherical (" football " bomb), as in the case of the Krupp and the British 2-in. T.M., sometimes formed to overcome air resistance, as in the Dumezil types. In either case, attached to the base of the projectile is a rod which fits closely into the bore of the mortar - like the rod of a rifle-grenade - and may or may not be fitted with a gas-check disc at its end. The gun itself is either a solidly forged small cannon or a long stout tube, trunnioned at its breech end, and its mounting is supported on a wooden bed. It is fired either by friction tube or percussion lock like an ordinary piece of ordnance, or by the primitive device of lighting a length of match placed in a vent or touchhole. As the base or gas-check of the rod is in contact with the bag containing the propellant charge, the pressures developed in the bore are comparable to those in a regular howitzer, and it is necessary not only for the gun to be stout but for the seating of the rod in the bomb base to be solid and cup-shaped, lest (as sometimes happened) the shock of discharge should drive the rod into the bomb before the inertia of the latter has been overcome. All stick-bombs, owing to the air-drag of the stick, and in the Dumezils and some others to the steadying effect of external vanes, fly nose first, and can be used with ordinary percussion or instantaneous fuzes provided the arming resistance of these is adjusted. Of this class, the most widely used was the Dumezil, designed by General Dumezil, in substantially its final form, as early as June 1915, and subsequently used by the French, Italian, Russian (in a modified form) and American armies, though declined by the British. The " Dumezil No. 2," here described was the standard medium trenchmortar of the French army throughout the last three years of the war. It is simple and easily transported and assembled by unskilled personnel. The mortar (fig. 1) is a stout cannon of forged steel (I) with simple vent-firing and rear trunnions. The maximum pressure with the heaviest bomb is 16 tons to the sq. in. The trunnions (2) are massive and bored through transversely to take a carrying bar or axle. It rests, when assembled for firing, in trunnion seatings formed in the inner parts of two cheek-pieces (4), which are heavy castings with accurately fitting inner faces. The foreparts of these are moulded upward to form elevating arcs forming a collar (3) on the gun slide, the gun being secured at the desired angle of elevation by screwing home the clamping screws. The cheeks (4) carrying the gun rest in a trough (5), attached to the back of which is a curved plate. This curved plate butts against a similar curved plate (10), which is jammed firmly against the back wall of the trench or emplacement. The mortar can thus be laid for direction by sliding the back-plate of the trough (5) along this back-plate (to). The bed, in which the system rests without being attached, consists of three planks (8, 8, 9). The system may be moved without being taken down, by means of wooden truck wheels attached to the axle (6) which is passed through to the sides of the trough, the cheeks and the bored trunnion. These accessories were, however, not much used in practice, as only 4 to 5 minutes are required to bring up and reassemble parts in a new position. Various methods of indirect laying for line were employed, as well as direct laying by periscope (excluding axle and wheels). The weights of the various parts are as follows: - mortar, trunnions and elevating collar 165 lb.; two cheek pieces, 1431 lb. each; trough 132 lb.; wall back-plate 106 lb .; three planks 128 lb. Total weight in action 818 lb. The stick-bombs vary in weight from 35 lb. (burster 131 lb.) to 99 lb. (burster 504 lb.). The earlier types, as in the 99-lb. bomb of fig. 2, had three vanes; later, as in the 40-lb. bomb of fig. 3, six were fitted. Some types had considerably more elongated bodies than those illustrated. With a charge of 4 oz., the 35-lb. bomb ranges to 715 yd. at an angle of elevation of 45°, the muzzle velocity being 263 f.s., and with a charge of 44 oz. a 68-lb. bomb, m.v. 220 f.s., ranges at the same angle of elevation to 490 yards. (C. F. A.) II. - Low-Pressure Smooth-Bore Trench-Mortars. Trench-mortars of this class are characterized by the fact that the pressure of the propellant gas is reduced by being allowed to expand into an " expansion chamber " of one form or another before beginning to take effect on the projectile. This device enables a thin-walled gun-tube to be used (instead of a true cannon such as the Dumezil above described) with considerable saving of weight. In some types, the firing of the charge was arranged to take place in a separate chamber which communicated by a channel with the expansion chamber, i.e. the breech portion of the gun-tube in which the projectile is seated. Such were the Aasen, the SuttonArmstrong, which was employed as a naval " bombthrower " ( see Ordnance: section Naval ), and the Temple. The last-named was distinguished by possessing a silencer attachment, which was considered by some authorities as a desirable addition in the period of short ranges and very advanced emplacements. Of more importance in the history of the World War are those types in which the strong-walled "combustion chamber" does not form a separate component, but is included either in the base of the guntube (as in the Batignolles type) or the base of the shell (as in the Stokes). In both of these, the " expansion chamber " is formed automatically by the fact that only certain projections from the shellbase, and not the base itself, rest on the bottom of the bore or chamber-shoulders when in the loaded position. The principal representatives of the class are the French Batignolles heavy trench-mortar, used also by the British, Italians and Americans, and copied, with modifications, in certain German patterns, and the British light Stokes mortar, which, with its derivative the medium StokesNewton, were used by the British and American armies. The Stokes Mortar, invented by Sir Wilfred Stokes early in 1915, was considerably improved in the course of the war as the result of experience with the weapon itself and with trench-mortars generally. It was first used in battle at Loos, Sept. 25 1915, when a few 4-in. tubes on bipod mountings, with strawboard-bodied shell, improvised at short notice, were employed for firing smoke shell; but by the battle of the Somme (July i 1916) both 3-in. and 4-in. mortars (the latter specialized for gas and smoke projectiles) had been issued in large numbers. Thereafter, to the last phase of the war, in which its lightness enabled it to do useful service as an " accompanying " piece, it satisfied all expectations. Each British infantry brigade of 4 or 3 battalions included a battery of 3-in. Stokes. Their principal characteristic was automatic ignition. Although it is believed that the first record of automatic ignition in trench-mortars, where the projectile carried its own propelling charge and igniter attached to the base of the bomb, existed in an early patent taken out in Germany by Messrs. Krupp, no practical use seems to have been made of this, and the first application of the theory of dropping a bomb of this nature down the bore of a mortar, so as to fire the charge and eject the bomb upon impact with the base, was that put forward by Sir Wilfred Stokes. The bomb in its first service form (fig. 4) had a container screwed on to the base, and this took a 12-bore sporting cartridge, the percussion cap of which, after the bomb had slid rapidly down the bore, impinged upon a striker fixed in the base of the mortar. In the 6-in. medium mortar (Stokes-Newton), developed later in the war, the principle of the fixed striker was adhered to, but both the mounting and the projectile differed entirely in design. The barrel of the 3-in. Stokes mortar (fig. 5) consists of a light seamless steel tube (A) drawn down at the base end, which is bumped into a semicircular form having a slight projection in the centre of the axis of the bore. This projection is drilled and threaded to take the striker (H), which, when screwed home, projects into the bore; the size of the combustion chamber is regulated by the extent to which the striker protrudes into the barrel or bore of the mortar. A cap (G) is screwed over the outside of the projection to take the set-back of firing. This cap, which is made of steel, rests in a small depression in the base-plate (C), which is fixed in the ground approximately facing the objective, and at a convenient angle, and has several such depressions placed in an arc to provide for changes of direction. The thin tube or barrel of the mortar has a smooth bore; it is supported above the centre of gravity by a pair of folding legs (B), between the apex of which (when open) and the barrel are the elevating and traverse gears, the latter being attached to the barrel by means of a steel band (see fig There is no attempt to take up or absorb mechanically the setback on firing, or the recoil, as the low combustion pressure renders this unnecessary at the ranges used.    As already noted, the 3-in. Stokes was in the British service set, apart for the firing of high-explosive bombs (although smoke-pro FIG. 2 FIG. 3 ducing bombs were added later), while the 4-in. mortar was reserved for gas, smoke and incendiary projectiles. The weight of the 3-in. bomb was given at Io lb., and of the 4-in. at 25 pounds. The design of the mortar, as between the two types, was only varied in so far as the difference in size rendered this necessary, and the same is substantially true of the design of the bomb. Steel is used in the 3-in. and both steel and cast iron bodies in the 4-inch. The first service patterns of bomb, and all subsequent ones up to the introduction of the vaned bomb in the last days of the war, have a cylindrical body, which is provided with 2 bands or " guides " as far apart as the wall of the bomb permits, preferably one at each end of this (fig. 7). The object of these guides is to ensure that the percussion cap falls accurately upon the striker after the bomb has travelled down the inside of barrel. The guides also eliminate friction during the descent of the bomb; windage has to be allowed for (i.e. sufficient space to permit the air compressed by the bomb in its descent to escape between the guides and the wall of the barrel). The windage provides an escape for the surplus air and ensures that the acceleration due to gravitation will drive the percussion cap with sufficient force on to the striker to cause ignition. In the 3-in. and 4-in. service designs the working chamber pressure is limited to 2 tons per square inch. At this pressure a range of 1,250 yd. is obtainable with the cylindrical bomb, when using the full propelling charge. This charge is obtained by placing rings of cordite round the exterior of the cartridge container, the container being per forated with a number of small holes, through which the gas from the cartridge escapes into the chamber, thus igniting the cordite rings in passing. The steel bomb is made up of ordinary commercial lap-welded steel tubing, cut to the desired length, and of the forged steel head and base which carry the guides and the cartridge container. As this mortar is not rifled, the bombs (except in the vaned patterns developed later) turn over and over in flight. If then, a burst or impact is desired, fuzes of the ordinary type which require nosefirst impact will not serve. A type of fuze was, however, designed, known as the Allways fuze (see Ammunition: section Fuzes ), which operates whatever the direction of fall. When time fuzes are required, either for air burst or for delay-action after impact, or because no Allways fuze is available (as was the case for a considerable period in the war), the arrangement most commonly adopted is that seen in fig. 7, viz. a " pistol," which is practically identical with the ignition device of the Mills grenade (see Grenade). The control of the bomber's hand over the lever is here replaced by that of a pin, which secures it till the moment of discharge, when the pin sets back and the lever is free to fly up. Bombs with vanes have been designed to obtain greater range and accuracy. As, these fly straight, head on, air resistance is diminished. These bombs are stream-lined as far as is possible, while allowing for the guides to be sufficiently far apart for accu- ‘Pi f ` I racy in impinging upon the striker. An addi tional margin of inaccuracy in descent down the bore of the mortar is provided for by fitting a cap which holds the needle point over the end of the cartridge, so that, no matter where this hits the striker, the needle will ignite the percussion cap. Safe ty against accidental dropping is provided - by designing the vanes to extend slightly beyond this cover. With vaned bombs, of course, normal types of fuze can be used. Generally speaking, high-explosive, smoke and gas bombs are all designed to explode upon impact, while incendiary bombs are designed to function in the air as nearly over the objective as possible. The Stokes-Newton 6-in. T.M. is similar, so far as the barrel is concerned, to the Stokes 3-in. and 4-in. A much stronger bedplate, however, is required owing to the increased weight of the projectile and the greater range, and the mounting is quite unlike that of the smaller weapons. Both direction and stability are obtained by means of lugs set radially round the outside of barrel, about midway, and attached to rings in the bedplate. These lugs can be lengthened or shortened by means of turnbuckles in the centre, thus obtaining elevation or depression and traverse at the same time. This method is slower than that used in the 3-in. and 4-in., but has the advantage of tying the mortar well down to the bedplate and ensuring stability. A somewhat similar device, providing for elevation only, is found in certain German and Russian trench-mortars. The projectile of the Stokes-Newton is similar to the cast-iron vaned bomb of the smaller weapons. It has steel vanes which are placed in the mould and become part of the casting. The propelling charge is guncotton, and this is ignited by a shortened service rifle cartridge, instead of the 12-bore cartridge which is used in the Stokes cylindrical bomb. This bomb is an adaptation of that of the French 240-mm. described below. The Batignolles 240-mm. (9'45-in.) Heavy T.M. is perhaps the most elaborate of those trench-mortars which stood the test of war. It was brought out in 1915 by the Batignolles Company of Paris, and first used in a great battle in the Champagne offensive of Sept. 25 1915. The model described is the earlier trench type. Later, the piece was lengthened and provided with less primitive firing arrangements. The model finally adopted in 1916 by the British War Office as the standard heavy trench-mortar also had different firing arrangements and a periscopic dial-sight.  The 240 court de tranchee, as this model is officially styled, consists of four main parts, the piece, the carriage, the baseplate, and the platform (fig. 8). The piece consists of two sections screwed together; the lower section, which has very thick walls, contains the chamber proper, in which the propellant charge is housed, and (in this model) an aerial vent to take the 12-secs. length of Bickford fuze which communicates the flame from the gunner's portfire to the powder primer of the charge. The upper or front end of the chamber is not " choked " but on the contrary opened out so as not to impede the rush of gas into the broader " expansion chamber," or lower part of the thin-walled tube. This thin-walled tube contains the vaned bomb (fig. 9), which unlike those previously described in connexion with the Dumczil trench-mortar, has its four vanes exactly in prolongation of the body. This arrangement not only enables the whole of the projectile to enter the bore, but ensures Cross stay Strap nut Traversing screw Nut of ele screw Yoke Large bevels Gear coverer Trunnion standard Set pins Large fork (right hand) Tubular leg Swivel bolt Cross stay bolt Adjusting lug Elevating gear Gear cover set screw Small bevel Bevel pin Elevating handle Small fork (left hand) Centre lug Right hand foot Left hand foot FIG. 6 .-Periscope screw Strap v Saddle t o Linch pin Traversing g FIG. 7 the maintenance of a free expansion chamber as the tips of the vanes, and not the base of the bomb, rest on the curved shoulders of the chamber proper. The bomb is of steel, thin-walled, and its body is built up from three pieces by autogenous welding, the cruciform vanes being secured to the body in the same way after being riveted to each other. A delay-action fuze only is used. With this, the powerful bomb, weighing 192 lb., of which 101 lb. are high explosives, will demolish thirty linear feet of trench work, break clown all but heavily protected dugouts, and make a crater in compact clayey earth 10 ft. deep and 30 ft. across. The piece is rear-trunnioned, the trunnions being firmly held in their seatings in the base of the carriage by a locking device. The carriage consists of a bottom-plate which contains the pivot-seating and the trunnion-seatings, and two side-brackets which are formed at their top edges as arcs for giving elevation. These arcs are toothed, and into them gear small pinions on a cross-shaft secured to a collar on the piece. Below this cross-shaft, and similarly secured to the collar, is another cross-shaft, the ends of which engage in slots in the side brackets of the carriage and carry the clamping arrangements by which the piece is secured rigidly to the carriage when the arc-and-pinion gear have brought it to the desired elevation. The elevation limits are 54° (with certain precautions 45°) for maximum range, 75° for minimum. On its underside the bottom-plate of the carriage has an ingenious arrangement of locking sectors which, when the carriage is placed over the pivot on the baseplate and given a partial turn, engage in a locking-ring on the face of the baseplate. (The ring originally admitted of all-round traverse, but this was later restricted to one of 18° each side of the mid-line, so as to avoid slantwise strain on the platform.) The baseplate is almost square and has on its upper side the locking-ring and pivot above mentioned. From its underside six vertical flanges project downwards. The platform is made up of five heavy square baulks, iron-shod and fitted with distance pieces so that, as they lie in position in the shallow, levelled pit, the four inner flanges of the baseplate can enter between them, while the two outer flanges fit over the outer baulks. Latches on both ends of each baulk engage with projecting tongues on the baseplate. Thus baseplate and baulks together form a steady unit in firing. The unit is further steadied against the horizontal component of the thrust by being wedged, back and front, against end-boards placed against the walls of the pit. The piece is laid for direction by an auxiliary aiming point, any suitable dial-sight being adaptable to the mounting-means of one or another form of dial-sight, a clamp on the bottom-plate of the carriage binding the latter in the desired position of traverse. All the parts are equipped with sockets for lighting-handspikes, except the piece itself which is carried by two staves passed through the two parts of carrying rings seen in the drawing. But movement in the trenches is as a rule by means of iron barrows pushed by hand. One barrow takes the mortar upright, another the carriage, a third the baseplate and accessories, while the baulks and end-boards are carried by hand. The weights of the short 240-mm. are as follows: mortar 485 lb., carriage 425 lb., baseplate 510 lb., platform baulks 132 lb. each. Total weight in action (exclusive of wedges, steadying pickets, etc.) 2,080 lb. The loaded weight of the heaviest barrow (baseplate, etc.) is 943 lb. The maximum range of the 192-lb. bomb with a propellant charge of 1 lb. 9* oz., is 1,125 yd. at 45° elevation and 1,045 at 55°30'. The maximum pressure in the bore is slightly less than 1 ton per sq. in. (150 kgm. per sq. cm.). The lengthened 240-mm. (breech-loading and percussion-fired) ranged with a 179-lb. bomb to 2,265 yd. (m.v. 476 f.s., maximum pressure 3,700 lb. per sq. in.), using a charge of 2 lb. 13 oz., but it required a heavier and more elaborate platform. A still more powerful weapon of the same class was the 340-mm. (13.4-in.), which required a concrete bed and a light-railway track for supply. This carried a 430-lb. shell (high explosive burster 205* lb.) to a distance of 2,250 yards. Pneumatic guns, as possessing a high-pressure reservoir and a lowpressure gun chamber, should also be included amongst the lowpressure class of trench ordnance. Owing to their silence and invisibility in action, they possessed marked advantages over the earlier forms of trench-mortar using explosive propellants. But their low power, their complication and liability to get out of order, and as regards some models, their entire dependence on a special form of supply (air or carbon-dioxide bottles) disappointed expectation; and of many ingenious designs put forward in the different belligerent countries, one only was consistently employed in the field. This was the French Brandt, classed as a light trench-mortar, which could obtain its pressure either from a bottle or from a motor-car pump. Its first model, which had a tripod mounting, weighed 484 lb. for the gun, 352 lb. for the tripod, and 70* lb. for the box of accessories and pumps. A later model, firing to a fixed angle only, was much lighter. It threw a 12-lb. bomb, or rather grenade, very accurately to a distance of 250 yd. but, although much greater ranges were obtainable, the accuracy fell off rapidly beyond that figure. (C. F. A.) III. - Rifled Trench-Mortars. The Germans were the first to produce an officially designed model of trench-mortar ( Minenwerfer ), and these weapons were used in the earliest sieges of the war. Although this gave German designers a long start in the competition, it did not save the German army from passing through the same phase of crude improvisations, which the French and British armies had to traverse. Bored-out shell mounted on blocks, old bronze siege mortars, experimental pneumatic mortars, and various smooth-bore types all figured in the armament of the German trenches for the first years of the war, and it is not till 1916 that the standard types are found in very large numbers. Thereafter, with the sole exception of a minenwerfer copied in principle from the Batignolles 240-mm., the standard types alone were used for general battle and trench service. The older types, so far as they survived, were practically reserved for throwing gas-bombs and other special projectiles. All the standard types of light, medium and heavy minenwerfer are rifled, and are derived from the pre-war service weapon. Modifications during the war were few, and did not affect the main elements of the design. They were principally two - the lengthening of the barrel in all three classes, and the adaptation of the light type to a direct-fire carriage, which enabled it to be used with conspicuous success as an " accompanying gun " in the semi-open warfare of 1918. The models selected for description here are the original model of " medium," the new or 1916 model of " heavy " and the light type with and without direct-fire carriage. Rifled trench-mortars were not used in any of the Entente armies. The characteristic of the German rifled trench-mortar in all forms is that, unlike the stick-bomb weapons and the low-pressure weapons which are radical departures from ordinary artillery practice, they are designed essentially as siege howitzers of reduced weight and power. Recoil-gear is provided, but of a simpler kind than the intricate combinations of elements necessary in a howitzer of high velocity and recoil energy; similarly, to ease the strain of discharge, by reducing the power necessary to propel the projectile, the driving band of the shell is " engraved " in advance. But the arrangement of piece, cradle and buffer, and the form of the shell, is in accordance with the conventional artillery practice.  The " old " model medium trench-mortar (fig. io) is a short, thinwalled howitzer of 17-cm. (6.69-in.) calibre, rifled with 6 shallow grooves of uniform twist, I turn in 26* calibres. The length of the rifling is 3.3 calibres. It is muzzle-loading and has percussion-firing gear placed axially on the breech. It is mounted in a ring-cradle which carries, above and below, a combined buffer and spring recuperator of simple type. The piece slides back and forth in the cradle and has the pistons attached to horns above and below the breech. The cradle is centre-trunnioned and the trunnions rest in seatings in a top-carriage of the usual form. The left trunnion car Fi g. 9 ries an elevating arc actuated by a worm-shaft and handwheel on the carriage. This trunnion also carries a panoramic sight (not shown in the illustration), mounted so as to slide on an arc which renders its position independent of the gun elevation. The baseplate, which is of steel, has longitudinal and transverse spades or flanges to enable the mounting firmly to be bedded on the ground. In the forepart, the baseplate has a vertical pivot and in the rear part an arc, which enables the top carriage to be traversed 121° either way from the centre line by means of the handwheel seen in the illustration. As in all German rifled trench-mortars care is taken to house in gearing and mechanism so as to keep out mud and dirt. The weight of the whole system in action is 1,064 lb. and the maxi mum range, with a 109-lb. shell (burster 241 lb.), is 980 yards. For transport, wooden wheels are fitted to axles on the bedplate and a handspike with a socket formed at the back of the same. The " new " model of medium minenwerfer is slightly longer (3.8 calibres rifled length), weighs 1,232 lb. in action, and ranges to 1,250 yd. with the same shell. The heavy minenwerfer, new model, shown in fig. II, is similar in all essentials of design to the above, but like other new models longer than the original model of its class. The details, such as the sight and the traversing gear seen in the illustration, and the elevating gear, etc., seen in fig. 10, are common to old and new models of medium and heavy. The new model heavy has a calibre of 245 mm. (9.8 in.) and has a rifled length of 4.54 calibres. It weighs in action 1,693 lb. and with a 210-lb. shell (103-lb. burster) ranges to 990 yards. The old model has a rifled length of 3.1. calibres and weighs in action 1,362 lb.; with the above shell it ranges to 612 yd. only. In the light minenwerfer, 7.6-cm. (2.9-in.) calibre, of which the " new " model is shown in fig. 12 and the direct-fire carriage in fig. 13, the piece, buffer and recuperator system and bedplate are similar in general to those of the medium and heavy types. But the topcarriage design is entirely different. The ring-cradle (which carries the buffer system as in the other types) is continued on each side to form arms which at their extremities are traversed by an axle, or through trunnion-bar, a few inches above the baseplate level. This bar rests in seatings in a very small intermediate carriage which traverses (through a circle) round a pivot in the bedplate. In the forepart of this intermediate carriage is another cross-axle which at its middle is formed as a socket, taking the foot of a stout elevating screw. This elevating screw (which is cased in leather to protect it from dirt) is clearly seen in fig. 13. It supports the weight of the cradle and piece, to which it is jointed, and elevation is given by screwing up or down. The weight in action of this model is 312 lb., the rifled length of bore 5.2 calibres, and the high-explosive shell weighs only 9 lb., and, comparing these proportions to those of the heavy and medium shell, it is not surprising to find that it ranges to 1,422 yards. The " old " model was somewhat shorter and lighter, and ranged to 1,150 yd. with the 9-lb. shell. The light minenwerfer, which is also known as the " Ehrhardt," was a very successful weapon, and every German infantry battalion had by 1917 a " light minenwerfer section," consisting of 4 of these pieces and a number of the "granatwerfer " described under Bomb Throwers. In 1918, in preparation for the expected resumption of " open " warfare, the Germans on the western front adapted the light minenwerfer for service as a direct-fire short-range gun of accompaniment for use against undisclosed machine-gun nests and other defences that might be met with in the course of a deep advance. For this purpose the bedplate, already provided with axles, was fitted with higher (29-in.) wheels, and a trail with trail spade was bolted to the small intermediate carriage described above. This trail is peculiarly arranged in the forepart. The cross-axle, or through trunnionbar, which, in the trench-service mounting, connects the ends of the cradle arms to the intermediate carriage, is, in the direct-fire mounting, connected to a framework in the trail which can be raised or lowered, thus enabling the cradle and mortar, always supported in front by the elevating screw, to assume either the horizontal or slightly elevated position with trunnion-bar high, or the quasi-vertical loading position (shown by dotted lines) with the trunnion-bar low. The motion of the framework in question is about a transverse axis contained in the trail and is controlled by a shifting level. Traversing is still about the pivot in the bedplate, and is managed by moving the point of the trail (by means of a small lever) along the broad arc-shaped spade member. The limits of this traverse, viz. with spade bedded, are I I. 8 ° either way from the middle-line. The maximum range with the 9-lb. shell in the direct-fire position high-trunnioned (elevation 38°) is 995 yd., but all angles between 34° and 75° may be obtained by transferring the trunnion-bar to the low position and proceeding as its high-angle platform fire. Both platform-fire and fire from wheels is possible in the high and low positions alike. In movement, the system is either man-drawn or limbered up to a two-wheeled cart drawn by one horse. IVDirect-Fire Trench Ordnance In spite of the great defensive powers revealed by the machinegun in trench warfare, certain local-defence needs made themselves felt in that type of warfare which the machine-gun of rifle calibre could not satisfy. In consequence, a variety of trench-guns were designed or adapted for emplacing as " forward " guns, or " infantry " guns. It cannot be said that this class of trench ordnance possesses any generic characters. A few were specially designed but the majority were field or small naval guns cut down and mounted on low carriages. Captured guns were frequently adapted for this service, when a large enough supply of ammunition and pieces was available, and also hooded quick-firing guns of the 57-mm. class taken from fortress armaments, in which formerly they had figured largely as a standard close-defence armament. Later on, these forward guns were sometimes made mobile again for use as guns of accompaniment. None of these converted types, however, need be dealt with here, and it will suffice to mention more particularly the 37-mm. gun (of French origin, but used also by other armies), not so much because it is representative of a class - which is too miscellaneous for any member of it to be regarded as such - as because it was used on a large scale in the war. It is a direct-fire quick-firing weapon, short in barrel length, mounted on a lowwheeled carriage and provided, as is a field gun, with a shield. It was laid over open sights and fired small, high-explosive shells with percussion fuzes similar to those of the " pompom," which were effective against machine-guns, etc., under light cover. The dimensions and weights of the Russian model of the 37-mm. (which is provided with the recoil-absorbing rubber discs commonly found in Russian designs) are as follows: - calibre 37 mm.; weight of the system in action 396 lb.; of the gun, breech and lock alone 864 lb.; and of the pointed shell with base-fuze and burster 1.1 lb.; m.v. 1,450 f.s.; max. range on the sights 3,500 yards. In their later evolution, many of these miscellaneous trench-guns became anti-tank guns. (C. F. A.) Copyright Statement These files are public domain. Bibliography Information
Chisholm, Hugh, General Editor. Entry for 'Trench Ordnance'. 1911 Encyclopedia Britanica. https://www.studylight.org/encyclopedias/eng/bri/t/trench-ordnance.html. 1910.  Ads FreeProfile |