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 10 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.
PNMt
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 fric- tion 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
Penscope screw Strap
Strap nut Traversing screw
Nut of elevating
screw Yoke
Large bevel- Gear cover Trunnion standar Set pins
Linchpin Traversing handle
Gear cover set screw
Small bevel Bevel pin Elevating handle
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 fro the cartridge escapes into the chamber, thus igniting the cordi 1 rings in passing.
The steel bomb is made up of ordinary commercial lap-welde steel tubing, cut to the desired length, and of the forged steel hea and base which carry the guides and the cartridge container.
As this mortar is not rifled, the bombs (except in the vaned pa terns developed later) turn over and over in flight. If then, a burj or impact is desired, fuzes of the ordinary type which require nos> first impact will not serve. A type of fuze was, however, designe< known as the Aflways fuze (see AMMUNITION: section Fuzes), \vhic operates whatever the direction of fall. When time fuzes are required either for air burst or for delay-action after impact, or because d Allways fuze is available (as was the case for a considerable perid in the war), the arrangement most commonly adopted is that see in fig. 7, viz. a " pistol," which is practically identical with tl] ignition device of the Mills grenade (see GRENADE). The control c the bomber's hand over the lever is here replaced by that of a pil which secures it till the moment of discharge, when the pin get 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- 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
FIG. 7
1111^3 III Lilt L/l.VJLJlctll A MW lll^.i l^ull lyv.
lengthened or shortened by means of turnbucklcs in the centre, I lin obtaining elevation or depression and traverse at the same I inn This method is slower than that used in the 3-in. and 4-in., but ha the advantage of tying the mortar well down to the bedplate ;m< ensuring stability. A somewhat similar device, providing for eld vation only, is found in certain German and Russian trench-mortars
The projectile of the Stokes-Newton is similar to the cast-iro: vaned bomb of the smaller weapons. It has steel vanes whli placed in the mould and become part of the casting. The propellin charge is guncotton, and this is ignited by a shortened service rill cartridge, instead of the 12-bore cartridge which is used in th Stokes cylindrical bomb. This bomb is an adaptation of that o the French 24O-mm. described below.
The Batignolles 24O-mm. (p-45-tn.) Heavy T.M. is perhaps th 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 o Sept. 25 1915. The model described is the earlier trench Later, the piece was lengthened and provided with less primiii\ firing arrangements. The model finally adopted in 1916 by th British War Office as the standard heavy trench-mortar also ha( different firing arrangements and a periscopic dial-sight.
The 240 court de trancltee, as this model is officially styled, con sists of four main parts, the piece, the carriage, the baseplate, am the platform (fig. 8). The piece consists of two sections screwec together; the lower section, which has very thick walls, contains thi chamber proper, in which the propellant charge is housed, and (u this model) an aerial vent to take the 12-secs. length of Bickfon fuze which communicates the flame from the gunner's port I ; the powder primer of the charge. The upper or front end of th( chamber is not " choked " but on the contrary opened out so a to impede the rush of gas into the broader " expansion chain or lower part of the thin-walled tube. This thin-walled tub" tains the vaned bomb (fig. 9), which unlike those previous; scribed in connexion with the Dumczil trench-mortar, has its foui vanes exactly in prolongation of the body. This arrangemn only enables the whole of the projectile to enter the bore, but ensure:
