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ground. Further, trench warfare took unforeseen shapes. Grenades, trench mortars, bombs and man-to-man weapons, even clubs and daggers, became normal infantry arms in minor and subordinate combats, while in the battle proper it was the artillery and the machine-gun rather than the firing-line of rifle-armed infantry that governed the issue both in attack and in defence. Thus when, from the latter part of 1 9 1 6 onwards, the " break-through," with its sequel of free infantry fighting in the background of the broken-through trench systems, became the ideal of tactics, the main infantry weapon was inevitably the machine-gun in some form. And thereupon the machine-gun of the pre-war and early war period began to develop on two distinct lines the heavy machine-gun with its own role and characteris- tics (see MACHINE-GUN), and the light machine-gun or infantry machine-gun. When this evolution set in, the machine-rifle or automatic rifle (some forms of which were already in use as machine-guns, especially with aircraft) was more or less ready to take up the place allotted to it by tactics.

The light machine-gun or machine-rifle " infantry machine- gun " is a better designation than either for the class as a whole is differentiated from the heavy machine-gun, technically and tactically, by being: (a) portable by one man; (b) unprovided with a mounting in the proper sense; (c) as inconspicuous in action or movement as an ordinary rifle; and (d) limited for various reasons to short bursts of fire. On the other side, as against the rifle, it possesses: (a) fire power with which no hand-operated weapon can compete, which indeed is equivalent for some moments at a time to that of the machine-gun proper; (b) an accuracy that, while less than that of the heavy type, is greater than that of the rifle, owing to the absence of trigger jerk and disturbance of the firer by recoil and to the fact that a muzzle support is (usually) provided; (c) ease and certainty in the matter of fire control, a mechanical organ in the hands of one man being far more manageable in the confusion of battle than a squad of extended riflemen. These advantages it gains, of course, at the expense of being more cumbrous, more delicate in mechanism and more expensive than the rifle, and it requires a fuller ammunition supply, or may do so. Further, it lacks one of the characteristics of the old infantry firearm it cannot serve as the haft of a bayonet, and thus the infantryman ceases, at least for the time being, to be self-sufficing, and infantry organ- ization at its lowest level returns to the lyth-century form, in which a fire element and a shock element are combined in the tactical group rather than in the individual soldier.

The characteristics of automatic rifle and light machine-gun fire, which thus become the most important element of infantry tactics, are briefly as follows. (For convenience, the term " auto- matic rifle " will be applied to the lighter and that of " light machine-gun " to the heavier members of the class under con- sideration. The definition by weight adopted in the following article fixes the frontier between the automatic rifle and the light machine-gun at about 20 Ib.)

The trajectory of an individual round, whether fired from a rifle, an automatic rifle, a light machine-gun or a heavy machine- gun, is the same for the same ammunition and barrel character- istics, though its relation to the object aimed at will vary to some extent according to steadiness of man or mounting, smooth- ness or shock of recoil and other factors. On the other hand, the cone or sheaf of fire formed by a group of rounds will be denser with the automatic rifle and denser still with the light machine-gun than it is with a number of rifles representing the same volume of fire per unit time. The grouping of shots is densest of all in the case of the heavy machine-gun fired from a steady mounting.

In proportion, therefore, as the steadiness in position, due to man, ground or mounting, enables an automatic rifle or light machine-gun to group its shots more and more closely, these weapons tend to acquire more and more of the peculiar tactical powers of the heavy machine-gun the ability: (a) to support close-fighting infantry groups by overhead or acute flanking fire; (b) to pour a direct and intense fire into small but danger- ous posts of the enemy, such as machine-gun nests; (c) to enfilade

enemy trenches and harass bridge approaches, cross-roads, and other points of very small area by day or night. It may be admitted at once that no existing light machine-gun and, a fortiori, no automatic rifle, is fully capable of (a) and (c), and in particular of overhead fire or fire through intervals between moving or fighting bodies of friendly troops without endanger- ing them. However, in (b) the light machine-gun is ballisti- cally scarcely inferior to the heavy machine-gun. This is its true function, which it performs as a rule better than the heavy, because its mobility allows of a closer approach, easier observa- tion and freer choice of position. The automatic rifle also possesses this power in some measure, but the light weapon of the future to be evolved from the two types must, before unity of type is acceptable, be made quite as capable of performing this tactical service as is the light machine-gun of to-day. At present the automatic rifle seems to be looked upon in some quarters as a weapon to be used normally as a semi-automatic, firing perhaps 50 or 60 rounds where the bolt-action rifle would deliver 10 and to that extent economizing men, reducing con- fusion, and minimizing casualties in the firing line, but in the last analysis always a rifle in the tactical sense. Its automatic power is reserved for special emergencies, just as, at the beginning of the evolution of the magazine rifle, the magazine was regarded as a reserve of fire power added to a single-loader.

Considering, next, volume of fire, we can safely say that for practical purposes all automatic rifles and light machine-guns have or can be made to have the same rapidity of fire as the heavy machine-gun. The rapidity is purely a function of the design. Whether recoil-operated or gas-operated, the cycle of operations is gone through as fast as the mechanism can take up the motive impulse. On the other hand, the possibility of maintaining the automatic rate for long without damaging the mechanism depends on (a) the solidity of the working parts; and (/>) the capacity of the barrel to resist overheating. In both respects the light machine-gun and the automatic rifle are definitely inferior to the heavy. Solidity of working parts and the incorporation in the design of cooling devices both involve deadweight, and it is the designer's first object to eliminate dead- weight. In the automatic rifle not only are weights of parts lim- ited but cooling devices are omitted altogether. 1 The possibility of automatic continuous fire is therefore definitely sacrificed. In light machine-guns, on the other hand, the working parts are not greatly different in solidity from those of heavy machine- guns, and some form of cooling device radiator, circulator or both is invariably fitted. The extra weight translates itself into greater power of sustained fire. With a positive cooling system, such as the water-jacket of the German L.M. 6.08/15, the volume of fire from a light machine-gun is practically equal to that of a heavy, if tactical conditions allow of equal ammuni- tion supply to each. Even the air-cooled guns are capable of delivering many hundred rounds without a pause other than those for changing magazines or belts. It is true that the devel- opment of full fire power for several minutes continuously is exceptional and even very exceptional, and it is a matter of opinion how much importance should be attached to this factor relatively to others in the arm of the future. But it seems clear, in any event, that the infantry machine-gun which constitutes the backbone of the attack or the defence ought to possess, at least at the shorter ranges, that power of focussing a storm of bullets on the enemy's machine-gun group, nest, or other centre of effort as soon as it is located. Otherwise the attack or counter- attack must wait for the heavy machine-guns to come well up, or at least to wait till exact information as to the target and the situation has been communicated to them.

This line of reasoning would exclude the automatic rifle alto- gether but for certain other considerations. The blotting-out by destruction or neutralization of well or strongly posted enemy groups in key positions is not the only function of the infantry machine-gun. It prepares by its fire every local advance of the groups of its own side, whether against or past important hos- tile nuclei or against simple parties of infantry using fortuitous

1 Except in the Chauchat, which is on the border line as to weight.