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operated by hand by means of a bolt handle (95) ; and an accelerator which is in the form of a cam lever, which acts against the bolt and barrel extension during the forward movement of the bolt, helping to push the barrel extension and barrel forward as the bolt advances under the action of the heavy recoil spring.

The gun is provided with a trigger and handgrip, a shoulder butt and a bipod, which is attached to the trunnion (96).

The front sight (97) is very high, owing to the low position of the barrel in the receiver and to the feed mechanism in cover. A tubular sight with a hole about one-fourth of an inch in diameter is attached by a bracket to the side of the gun for close-range shooting and for tank work. It will be noted that several features of this gun were adopted in the L.M.G. 08/18.

In the German army Bergmann guns formed the armament of the so-called " Light Machine Gun Detachments," mounted units created in 1916 for the Rumanian campaign. The use of this gun, however, seems to have been discontinued towards the end of the war, the weapons remaining serviceable being handed over to Turkey.

FIG. 15. Bergmann Light Machine-Gun.

Machine Carbine-Pistols. The idea of securing more accurate shooting from a pistol by fitting it with a shoulder stock and lengthening the barrel is an old one, and one well-known modern example is the Mauser pistol (for description see 21.657-8). But while in the pistol proper, from the nature of the arm and its uses, all modern development has been in the direction of per- fecting the semi-automatic action (see PISTOL), there arose in the World War a need for some weapon lighter and handier than the rifle yet capable of developing an intensely rapid fire at short ranges. The outcome of this need was a class of firearm which at present has few representatives and no recognized generic title, but is very interesting. In the absence of an accepted designation, these may be called machine carbine-pistols.

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FIG. 16. Bergmann Pistol-Gun.

In this field the precursors appear to have been the Italians. The pistola miglialrice Fiat (Fiat mitrailleuse pistol) was largely used by them as a substitute for the light machine-gun, no doubt because extreme lightness both in the gun and its am- munition was essential in an automatic arm for mountain warfare. The " machine pistol " is fitted with a small shield which also serves as a mounting, though the weapon can be used in the hands, if necessary. It is double-barrelled, each barrel having a separate box magazine of 25 rounds above the receiver. It is gas-operated and air-cooled. The bolt and its dependent parts are supported but not positively locked on firing. It weighs 14 Ib. without shield, takes 9 mm. pistol ammunition, and is sighted to 500 metres. An outstanding feature is the very high rate of fire. Both magazines (50 rounds) are fired in two seconds, and with highly trained loaders and a full supply of magazines it is said that 1,000 rounds can be delivered in a minute. This ex- treme rate, in spite of certain advantages, militates against steadiness and accuracy, especially with so slight a mounting. Nevertheless, according to the Germans the weapon proved trustworthy and effective.

The Bergmann Pistol-Gun (fig. 16), on the other hand, was intended not to replace the light machine-gun but to provide

artillerymen and machine-gunners with a handy personal weapon capable of intense fire power in emergencies. It originated in the pistol proper. The German service pistol 08 (Borchardt- Luger) used by specialists, who were not armed with the rifle, was fitted with a snail magazine (see PISTOL) allowing of 32 shots, the wooden holster being attached to the handgrip as a shoulder piece as in the Mauser pistol above alluded to, if accurate fire was required. The success of this arrangement led to the intro- duction of the Bergmann pistol-gun (officially, Machine-Pistol 18 1.), which in spite of its name is rather a carbine than a pistol, as an infantry weapon pure and simple.

This arm shoots 9 mm. pistol ammunition at the rate-of about 540 shots per minute. The gun weighs 9 Ib. 6 oz. without the maga- zine drum, which itself weighs I Ib. 8 oz. empty. It is recoil-operated and air-cooled, and has an 8-in. barrel, protected by a casing per- forated to allow circulation of air. The magazine (32 shots) is of the snail type (see PISTOL). The breech mechanism is of the " blow-back " class in which on firing the inertia of the bolt, the compressing of the mainspring, and friction of the cartridge in the chamber momentarily hold the action firm. The gun fires when the bolt reaches its forward position as the striker projects through the face of the bolt, and is cocked when the mainspring is compressed and the bolt drawn to the rear. This has the advantage that the chamber is always left empty, but the forward movement of the heavy bolt after pulling the trigger is liable to disturb the aim. The gun is sighted to 200 metres only.

This gun was only brought into use just before the Armistice.

101 ... 103 99 100 102

FIG FIG

18 I Thompson Sub-Machine-Gun.

The Thompson Sub-Machine-Gun (figs. 17 and 18) is an inter- esting type of a very light portable automatic weapon which shoots a -45-calibre pistol cartridge. The action is semi-auto- matic or automatic at will. The rate of fire when used as an automatic is 800 to 1,500 shots per minute. The weapon is about 23 in. in length, weighs 7-5 Ib., and uses a straight magazine (fig. 18) holding 20 cartridges in staggered rows, or drum maga- zines holding 50 or 100 cartridges (fig. 17).

The novel feature of this weapon is the angular wedge breech closure which utilizes the force of adhesion developed by the heavy breech pressure to lock the breech. The principle, developed by Comm. Blish of the U.S. navy, has been briefly stated as follows:

" In any breech closure consisting of a breech plug in a suitable housing and having two pressure-resisting surfaces, the forward surface disposed normally to the axis of the bore, and the rear surface inclined thereto and bearing upon a suitable surface of the housing, the force of adhesion will under heavy pressure immovably fix the breech block, but at a comparatively small pressure (whose value de- pends upon the inclination of the two surfaces) the force of adhesion ceases to act and the breech block is rendered free to move under the influence of the forces then existing."

The principle permits the use of a very simple breech-locking mechanism, the essential element being a bolt (98) having an angular slot cut in the under side, into which the lock (99) is free to slide, and a housing or receiver (loo) having a slot (101) into which a projecting lug on the lock engages when the bolt is in its firing position. Under high pressure the lock firmly adheres to the receiver shoulder and