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Rh a 7-5 bombthrower. This design was subsequently altered to a /-5-i. rifled howitzer. Eventually a small number of bombthrowers and a large number of howitzers were made of this pattern, the non-recoil mountings in both cases being identical. In the design and supply of these two weapons,. the overruling question was rapidity of produc- tion, and no time could be spared on refinements of design or finish. The result (fig. 50) was a roughly finished equipment which, although it served its purpose at the time, would not be repeated. It is extremely simple in construction and consists of a rifled " A " tube, with screwed breech and trunnion rings. The breech mechanism is of a simple B.L. type with a riile-lock firing gear. The weapon is in reality a very simply constructed low-power breechloading gun. The 7-5 M.L. bombthrower is similar in construction to the howitzer but is smooth-bored and a breech plug is used instead of a breech ring. A simple sliding breech mechanism is fitted and the charge is contained in a small brass cartridge case. The bomb is loaded from the muzzle and is fitted with vanes.

FIG. 50. British B.L. 7-5-in. howitzer.

The mounting of both the howitzer and the bombthrower consists of a cast steel carriage, carrying recesses for the trunnions, which rests on the fixed pivot of the base plate. The lower surface of the carriage and the upper edge of the base plate are machined to form a training surface and the base plate is bolted to the deck. A strong all-round clip ring is fitted over the flanges of the base plate and the revolving carriage to hold the mounting to the base plate on firing. The effective blow transmitted to the deck on firing the howitzer on this rigid non-recoil mounting is large and necessitates very con- siderable strengthening to the ship's structure under the mounting. The elevating gear, as at first designed, consisted of a vertical screw, secured to a band round the breech of the gun and operated by suitable mechanism connected to the elevating wheel on the left of the mounting. On account of the distortion of the elevating screw by the firing stresses it was abandoned and a simple shoulder piece fixed to the gun itself, was adopted. A simple form of aperture sight is fitted. A rate of fire of 4 to 5 rounds a min. could be maintained with this howitzer; at one trial 20 aimed rounds were fired in 35 min. with an untrained crew.

The main object for which these equipments were designed was achieved, as no less than 650 of them were actually mounted afloat within a year of the design being called for.

The lo-in. R.M.L. bombthrower was a bombthrower of novel type which was evolved from a design produced by Messrs. Thornycroft (fig. 51). The bombthrower consists essentially of 2 parts, the explosion chamber and the barrel, the former being placed on top of the latter and secured to it by steel straps. The charge is burnt in a perforated combustion chamber secured inside the front end of the explosion chamber. The gases, after expansion in the explosion chamber, pass downward through a dowel in its rear end into the rear end of the barrel. The charge is contained in a small brass cylinder and is loaded at the front end of the explosion chamber, which is fitted with a simple sliding breech mechanism. The bomb is loaded from the muzzle and is fitted with six studs which engage in the rifling grooves in the barrel. The lo-in. bombthrower which was used in the British navy (the actual design of which was pro- duced by Messrs. Vickers) is built up of a number of parts. This was done in order to make use of the shell-making plant which was available at the time. The non-recoil mounting is similar to that of the 7-5 howitzer in general design but is fitted with a stronger clip ring and powerful elevating gear. At the trials of the first of these weapons difficulty was experienced in determining a satisfactory charge. Very high pressures, which appeared to follow no known laws, were experienced in the explosion and combustion chambers,

and it was only after a long series of trials that a suitable charge and design of combustion chamber were obtained by " trial and error." Though designed especially for rapid production to fulfill an emergency requirement, manufacturing difficulties rendered the results disappointing.

The n-in. howitzer was introduced in order to provide armed merchant cruisers and large vessels generally with a quick-firing anti-submarine gun of considerable size and firing a heavy pro- jectile. The howitzer is built up and consists of an " A" tube, jacket and breech ring. The breech mechanism is of the Asbury type and is fitted with a rifle-firing mechanism. The mounting is a recoil one of more elaborate type than those of the other howitzers and bomb- throwers, it being a roller-path mounting with cross-connected sights, hydraulic recoil, spring run-out and a loading tray geared to a quadrantal rack. The accuracy is very good, a mean error of only 17 yd. being obtained at 44 of elevation; and the errors in range at the lower angles of elevation are even smaller. Two reduced charges are used which also give good accuracy, and by using suit- able charges the projectile can be made to dive at a minimum range of 225 yd. A considerable number of these equipments were mounted in vessels employed on convoy duties during the war.

The 6-in. Newton bombthrower was mounted on gymbals to give free and elastic support to the gun. The gun rode in a spherical cast- iron dish, the breech end of the gun being just clear of the dish. On recoil the gun set back hard on the inner surface of the dish and, the latter being very massive, the blow on recoil was largely absorbed by it, only a light stress being transmitted to the deck structure. A central stud was fitted at the bottom of the barrel to form a stop for the bomb when loaded. The barrel was mounted in a sleeve which formed the trunnions and attached to the barrel was a control arm carrying the laying handles and sights. This equipment as a whole proved unsuitable for service afloat, but the bombthrower itself was an unsatisfactory weapon and this fact possibly obscured any good points which might have appeared in the principle of the mounting.

Heavy Stick Bombs. Early in 1918 it became increasingly evident that projectiles with a heavier bursting charge than thcjse in use in the existing howitzers and bombthrowers were necessary if any real 'damage was to be done to submarines. A heavy projectile which would dive at short ranges was required and this led to the intro- duction of the heavy stick bomb. A hydrostatic fuze is used in these bombs, to fire the bomb when it arrives at a prearranged depth below the surface. In all trials the accuracy was very good and it was found possible to use the same charge as when using the internal projectiles in the sa'me weapon, thus eliminating complications in supply and drill. The trials were extended with each weapon by firing the lighter bombs, with the same full charge, down to the bomb which contained a burster approximating to that of the inter- nal projectile of the particular weapons. Many trials were carried

FIG. 51. British lo-in. R.M.L. bombthrower.

out to perfect the fuzes and detonating arrangements of these large bombs, and supply in bulk was about to be made to the service afloat when hostilities ended.

During the last six months of the World War it became increas- ingly necessary to introduce some method of throwing a heavy explosive charge to a distance of 150 yd. or more. The use of the stick bombs was therefore applied to the smaller guns, and a series of trials, carried out in June and July 1918, showed that the same stick bombs as were used in the howitzers and bombthrowers could be fired from guns of 4'7-in. calibre and below. It thus became pos- sible to supply to these guns a projectile which contained a burster of the same order as that of a depth charge. Measures were at once taken to supply these projectiles generally, but unavoidable delays occurred in manufacture, and it was not till Nov. 1918 that issue of bombs of this class began on a large scale. (S. T. H. W.)