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on RIFLES AND LIGHT MACHINE-GUNS. The gun differs from the ground type in having the cooling system removed, in being supplied with a "spade grip "instead of the butt stock, and in having special air-craft sights fitted. The magazines used in the air differ from those used on the ground in holding 97 rounds instead of 47, and in being

FIG. 7. Lewis Aircraft Machine-Gun.

fitted with a counter showing the number of cartridges remaining. This gun is used as a flexible gun, and is mounted either singly or in pairs in the rear cockpit of two-seated aeroplanes. The mounting used for these guns, called, from the name of its inventor, the Scarff mount, allows easily controlled universal pointing of the gun.

Theory of Machine-Gun Fire. Machine-gun fire is usually applied in one of the following ways: (a) as direct fire, (6) as overhead supporting fire, (c) as indirect fire. Machine-gun fire falls under the classification of " direct fire " when the situation is such that the objective is in plain sight and the gun is pointed directly at it by means of the sights. Overhead fire occurs when the line of friendly troops is supported by machine-guns located at positions in the rear. If either the machine-guns or the enemy targets occupy a position sufficiently elevated with reference to the friendly troops, the curve of the trajectory allows the bullets to pass over the heads of the supported troops and descend on the enemy. The height of the trajectory is sufficient -at medium and long ranges to make it theo- retically safe to execute overhead fire when the guns, the enemy, and the supported toops are all on the same plane; but, in order to ensure the safety of the friendly troops, fire of this nature is not usually employed unless the target occupies a position relatively higher than that of the supported troops. The established method of deter- mining whether or not overhead fire may be safely executed is by the use of an arbitrary " safety angle " which is the minimum angle by which the line from the gun to the target must be above the line from the gun to the heads of the friendly troops. In employing this class of fire, careful control is necessary to ensure the safety of the troops being supported, and it is of prime importance to know when it is safe to begin firing over the heads of friendly troops, also when to cease firing before theiradvance has proceeded far enough to bring them into the danger zone. The practice in this regard varied in different armies and at different times during the World War. One British practice was to employ a safety angle of 30 min. for ranges up to 1,000 yd., and a safety angle of 60 min. (l) for ranges from 1,000 yd. to 1,500 yd. These angles are found by holding a 24-in. string to the eye and sighting past a card upon which are three lines. The first and second are 0-21 in. apart, and the first and third are 0-42 in. apart. At 24 in. these distances correspond to 30 min. and 10 min. respectively. Another British method is as follows : ( I ) set the sights for the true range and aim at the target; (2) without moving the gun, raise the sight 400 yd. and locate a point by aiming. This point is the danger point beyond which it is not safe for troops to advance while overhead fire is being executed ; (3) when the friendly troops reach this point, either cease firing or elevate the guns and fire behind the enemy's lines to harass his retreat. Indirect fire is fire aimed at some object other than the one it is desired to hit. One of the simplest kinds of indirect fire is night firing. Suppose that it is desired to control by machine-gun fire at any time during the night some point, such as a crossroad, which is in plain sight during the day. The gun is laid on the objective by means of the sights. Then, without moving the gun, the sights are changed so as to bear on some small object near at hand, called an aiming mark. As long as the sights are kept pointing at this aiming mark, the gun will be point- ing at its objective. For use as an aiming mark at night, a special apparatus is furnished, consisting of a metallic box with an electric battery and a small light. This is called the night-firing box. It has several holes in one side through which the light can shine to form aiming marks. In use, it is set up a short distance in front of the gun, in such a position that the lighted spots can be seen only from the gun position. The spots of light on the box are a measured distance apart, so_ that known changes in deflection can be obtained by shift- ing the aim from one spot to the next. Another case in which indirect fire must be used is when the target is not visible from the gun position. In this case the gun must be laid entirely by calculation. Before this can be done, the following data must be obtained : (a) the angle of elevation, which can be determined only when the range, or horizontal distance to the target, and the difference in height

between the gun and the target are both known. When these factors are known, the angle of departure corresponding to the given range is determined from a range table, and then the angle of elevation is obtained from it by adding or subtracting the angle of site, which is the vertical angle between the horizontal plane and the line from the gun to the target ; (6) the azimuth, or horizontal direc- tion of the target from the gun position.

EVOLUTION OF MACHINE-GUN TACTICS

Before the outbreak of war in 1914, the British army author- ities, with the exception of a small body of officers who possessed expert knowledge of the weapon, had devoted little thought or study to the development of machine-guns or machine-gun tac- tics. At that time the army as a whole undoubtedly mistrusted the machine-gun as a weapon. This mistrust was probably due in great measure to the indifferent results achieved with the Maxim gun during the S. African War (1899-1902), in which the gun frequently " jammed " at a critical moment, not from any fault in the mechanism, but from lack of knowledge amongst the personnel as to how the gun should be handled. The gun was not popular in the ranks, since its appearance was apt to attract hostile artillery fire on to the firing line.

The Russo-Japanese War clearly demonstrated the value of machine-guns both in attack and defence; and the Germans, as a result of their study of the fighting in Manchuria, multi- plied their machine-guns and organized them in companies.

On the outbreak of the World War, the machine-gun resources of the British Expeditionary Force consisted of a " section " of two machine-guns in each infantry battalion and cavalry regiment. The infantry section was armed with the Maxim 303-in., the cavalry section with the Vickers -303-^. gun. The war establishment of these sections was as follows: infantry section, one officer, one sergeant and 16 rank and file; cavalry section, one officer, one sergeant and 25 rank and file. By this date the transport in use consisted of a G.S. limbered wagon (two-horsed) which carried two guns and mountings with the necessary accessories and first-line supply of ammunition. In the cavalry section the gun detachments were mounted on riding-horses and the cavalry section was, therefore, more mobile than the infantry section. Pack-saddlery was carried to enable the sections to be taken into action on pack animals when necessary. A study of the British 1914 Training Manuals shows that the accepted doctrine as regards machine-gun tactics at that date was briefly as follows. The machine-gun was considered to be essentially a direct-fire weapon; it was not considered sufficiently reliable to carry out overhead or indirect fire. To quote Infantry Training (1914): " Machine-guns are essentially weapons of opportunity. The power of the gun is best used to develop unexpected bursts of fire against favourable targets "; and, again, " Owing to the liability of the mechanism to inter- ruption and the expenditure of the ammunition involved, the gun is not suited for sustained fire action." It was laid down that the machine-gun section formed an integral part of the battalion or regiment to which it belonged; but at the same time the " brigading " of sections was legislated for, and a brigade machine-gun officer was appointed in each brigade to command the sections when brigaded. The advantages and disadvantages of either leaving the sections with their battalions or of brigading them were stated, but no indication was given as to which was to be considered the normal method of employment, or as to the circumstances under which either method would best be utilized.

Soon after taking the field in Aug. 1914 it became apparent that the Germans were far ahead of the British in machine-gun tactics and organization; and, moreover, that a very great increase in the number of machine-guns in proportion to rifles was necessary. In Great Britain, the first step to remedy the deficiency was, towards the end of 1914, to increase the number of guns in the section from two to four. But the need for any alteration in methods of tactical handling was not yet realized by the British army at large; and since the machine-gun was considered to be solely a direct-fire weapon it was employed with the most forward troops, and, in defence, was almost invariably positioned in the front-line trench.