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Gun-Carrying Tanks are here considered as gun-carriers. A war-time tank normally carried two short 6-pounder guns, one on each side, and 200 rounds of ammunition; it could carry another too rounds if required. If the tank were made larger, it could carry a i2-pounder or i8-pounder gun inside. When the gun is put outside, on the top, the machine ceases to be a tank and becomes an automobile gun-carriage or a caterpillar carrier; these have been discussed on pp. 248-49.

The volume of fire from a tank is not sufficient to constitute a decisive factor in the combat. Fire with shrapnel and time fuze from a moving tank would be a waste of ammunition, and the tank would not last long if it stood still. The small H.E. shell is nearly useless against men in the open, and the case-shot which the tank carries is effective only at very short range. The guns of a tank cannot be expected to engage infantry manning a trench parapet, and keep down their fire, except when the tank succeeds in getting astride of the trench and firing down it to right and left. Even then the effect is rather moral than material, since the infantry are protected by the traverses and indentations of the trench, which are specially designed to prevent enfilade. Practically, there are only two things that the guns of a tank can do, but these are both im- portant. They can destroy an enemy tank, and they can put a H.E. shell into a machine-gun emplacement at short range, long before a message could be got through to a field gun a mile behind. For both these purposes the 6-pounder gun is sufficiently powerful, though it is possible that thickly armoured tanks may be introduced which will require a heavier weapon to pierce them. Quite apart from its gun-power, the tank supplements and sometimes replaces artillery fire by its power of crushing obstacles, notably barbed wire and iron palisades.

It remains to be considered whether the tank is a satisfactory substitute for the infantry gun of accompaniment. The ad- vocates of tanks anticipate that in future an infantry attack will be carried out on the following lines: In front of all is the creeping barrage, closely followed by the infantry and the light tanks (" cruisers ") armed with machine-guns and possibly 6-pounders; behind these come i8-pounders or heavier pieces on armoured automobile carriages (" battleships "), and small fast caterpillars (" destroyers ") carrying tank-stopping ma- chine-guns. Just before the assault the " cruisers " dash for- ward in advance of the infantry, supported by the fire of the " battleships " and escorted by the " destroyers." The " battle- ships " also deal with machine-gun nests and strong points that have escaped the barrage. As the infantry continue their advance, the motor-drawn guns behind, which have been form- ing the barrage, advance by echelons to fresh positions behind the infantry, and carry the barrage forward.

Supposing an attack on these lines to be carried straight through, no infantry guns, capable of fighting on their own wheels, would be required. But it is objected that if the in- fantry attack were checked, as is inevitable at times, their only guns of accompaniment would be the large and conspicuous " battleships," which are very vulnerable when standing still. The same objection would apply in a retreat, which is a series of halts to check the enemy. It would appear, therefore, that the infantry gun must be separable from its motor, so that it can fight, and conceal itself, on its own wheels. Neither the " cruiser " nor the " battleship " tank satisfies this condition, but it may possibly be desirable to introduce a tank which shall carry a light gun to the fighting front, dismount it, hand it over to the infantry, and then advance on its own account, with its machine-guns, as a fighting tank. No tank of this kind has yet been tried, and moreover there is no present prospect of the large and expensive armoured " battleships " being provided in any army. Manufacture on the large scale would probably not begin till the outbreak of war. In the meantime, the infantry gun of accompaniment will have to be developed as an infantry weapon, independently of the " land fleet." Whether it should be motor-drawn, motor-carried, mule-carried or man-handled is still an open question. Many officers are in favour of a gun dra-n by a small tractor, to take it as far forward as possible;

the gun to be light enough to be man-handled when the tractor fails. The American infantry howitzer referred to above realizes this idea, except that it is carried instead of being drawn.

Artillery Fire at Tanks. The best means of stopping tanks is still an open question. It would at first seem a simple matter to make direct hits on them, but in practice the enemy's barrage and bombardment interpose a screen of bursting shells behind which the tanks can approach unseen. Moreover, it is not easy to find a position affording a good view, from which the gunners can lay over the open sights, within 2,000 yd. of the front line. Indirect laying is too slow for moving objects. When preparing to meet the German advance of March 1918, the British plan was to hide a number of field guns in or close to the front line, which were to keep silent till tanks appeared, and then fire on them. These guns were never heard of again; they were all destroyed by the intensive bombardment which preceded the attack. In some cases, land mines were buried under the barbed wire entanglements to prevent the tanks from " rolling them out," but these mines rarely survived the bombardment. They might be useful, however, if the enemy attempted a sur- prise attack with tanks without a preliminary bombardment. The best means of resisting a tank attack on an entrenched position would appear to be the provision of numerous small anti-tank guns in the trench area, as described below.

In mobile warfare the conditions are somewhat different; in the autumn of 1918, when the British alone used 2,000 tanks, many of these were destroyed by the German rear-guard bat- teries, and by concealed guns left behind for the purpose. The Germans used heavy single-loading " anti-tank rifles," pending the introduction of large calibre " anti-tank machine-guns," and it is stated that a tank-stopping rifle grenade, fired from' the muzzle of an infantry rifle, has lately been produced. It would seem, however, that in open warfare the most formidable op- ponent of the tank is the enemy tank, and it is probable that a special type of light fast tank a " tank destroyer " armed with one gun amidships, or even with a heavy machine-gun only, will be introduced.

II. TRENCH WARFARE

The lessons of the first phase of the war had been the necessity for a high degree of mobility, the breakdown of direct liaison between infantry and artillery, and the weakness of permanent fortifications of old-fashioned type when attacked by modern guns. When the armies settled down to " sedentary " trench warfare, a fresh set of problems presented themselves.

At first, the trench system, however multiplied in detail, was simple and continuous in the ensemble; in 1915 a system often consisted of three lines or skeins of trenches half a mile apart and connected by communication trenches. But, in the latter part of the war, different principles were followed, and a modern trench system is not a single strongly garrisoned line, in which the troops would offer an easy target to artillery, but a fortified zone two to three miles in depth. The front nearest to the enemy is not a continuous parapet; it is dotted with inter- supporting points of resistance, varying from a shell-crater holding three men to an armoured " pill-box " or a fortified " strong point " held by a platoon with machine-guns. The actual front trench may be a mile behind the front of the system, and in any case is not visible to the enemy. It is dug on a reverse slope when possible, as a field of fire of 100 yd. is quite enough for modern rapid-firing rifles and machine-guns. Even the front trench is often not continuous, but consists of short lengths arranged so that each can be enfiladed by guns, or more usually machine-guns, in rear. It is a chain of defences, rather than a continuous barrier. Behind the front trench is a network of fire trenches, strong points, and communication trenches from one to two miles in depth; this is a styled the " battle zone." Behind this is the second-line trench, which forms the front of the " reserve zone." Still further to the rear there may be second and third trench systems and reserve lines. The ground in front of the battle zone is the outpost zone, and is not in- tended to offer serious resistance. Its function is to screen the