Machine-Gun Tactics

by R. V. K. Applin

It will be seen that the 75 per cent., or effective zone, is deepest at 500 yards, and gradually decreases as the range increases up to 2,000 yards; beyond this distance it increases again in about the same ratio up to 3,000 yards.

The following formula will give the effective zone (75 per cent. of shots) approximately for all ranges up to 1,500 yards inclusive: 50,000 Range + 20. Example for 1,000 yards: 50,000 1,000 + 20 = 70 yards, which is the depth of the area swept by 75 per cent. of shots, or the “effective” beaten zone. For ranges beyond 1,500 yards this formula is useless, and after 2,000 the beaten zone increases in depth, while the angle of descent of the bullets becomes so steep that the “dangerous space” is reduced to a minimum; and consequently the zone beaten by 75 per cent. of shots is no longer the “effective zone,” and it will be necessary to get the target within the zone beaten by the nucleus, or 50 per cent. of the shots. This zone at 2,500 yards range is about 50 yards in depth, so an error in estimating the range of more than 25 yards over or under the correct distance will render the fire “ineffective.” Even at 1,500 yards the “effective zone” (75 per cent.) is but 60 yards deep, which only allows an error of 30 yards over or under the correct range—a very small margin, even when using a range-finding instrument, but without an instrument it is obviously impossible to “estimate” or “judge” the distance with sufficient accuracy to ensure bringing the “effective zone” on the target.

For ranges over 500 yards it is absolutely necessary to know the range accurately or to find some other method of bringing the “effective zone” on to the target.

The machine gunner may be likened to the fireman with his hose-pipe, whose object is to bring the base of his jet of water to play on a certain spot some distance away from the nozzle of his pipe. He does not trouble about the distance, he does not require to know the range; but pointing the nozzle in the direction of the spot he desires to strike, he elevates or depresses it until he observes the base of the cone of water falling on the right spot, and then he holds his pipe so that it continues to fall where he desires; he does not trouble about the smaller streams and drops of water that fall short or go beyond, but devotes his whole attention to keeping the nucleus of the stream—the 75 per cent. or 50 per cent. zone—falling on his “target.” In precisely the same way the machine gunner must look upon his stream of bullets as a stream of water from a hose-pipe, and his object must be to cause the centre of that stream to play on the target, or, in other words, to bring the effective cone of fire on the target so that it is the centre of the beaten zone. This can be done by “observing” the strike of the nucleus of the shots and altering the elevation accordingly. On favourable ground fire can be observed by No. 1 up to 800 yards, but No. 2 with the aid of good glasses can observe fire on favourable ground up to 1,500. This observation of fire is the best method of obtaining the correct elevation at “effective” ranges (i.e. 1,400 to 600), if the ground is suitable. The procedure should be as follows: The range should be “estimated” by No. 1, who should then adjust his sight for 100 or 200 yards less elevation than the supposed distance, and fire “groups” of 8 or 10 shots; No. 2 observing the strike of the bullets and saying “short” or “over,” as the case may be, while No. 1 alters the elevation between each group until No. 2 says “on,” when fire may be continued, still observed by No. 2, until the desired effect has been attained. No. 1 must be careful to fire his first group of shots short of the target, as they are much easier to locate than shots which fall “over.”

If the target is only visible for a short time, the groups may be “rapid,” but as a rule “deliberate” fire at the quickest rate should be used, and “rapid” only used when the range has been found. If the ground is not favourable for the observation of fire, or the range is too great, this method cannot be used, and it will be necessary to obtain the range by instruments; but it will not always be possible to do so, and it is necessary to find some other reliable way of ensuring that the target is within the “effective” zone.

Supposing the range to be estimated at 1,400 yards, the effective zone is about 60 yards in depth—therefore an error of only 30 yards in estimating the range can be permitted. There is but one way to overcome the difficulty, and that is by increasing the effective zone; and this can be done by using “combined sights,” thus making two or more beaten zones which touch each other and overlap where the effective 75 per cent. of shots of both ends.

There are two ways of using combined sights:

(a) The “single gun” method.

(b) The “battery” method.

In (a), with an estimated range of 1,400 yards, the sights will be set for 1,300 and aim taken; then the sights will be again set for 1,500 yards, but without altering the original aim, and then “rapid” fire opened and the elevating wheel slowly turned to elevate the gun until the 1,500 yards sighting is aligned on the target. The result of this operation is to sweep the whole ground from 1,270 to 1,530 yards with effective fire; and if an error of 125 yards over or under the correct range has been made, the target is nevertheless brought within the effective zone by the combined elevations used. This is the best method for sections or single guns, and a section can vary this by one gun using 1,250 yards elevation and working up to 1,400, while the other gun begins at 1,350 and works up to 1,550. The choice of the amount over and under the estimated range must depend upon the ability of the person estimating the range and circumstances of the case, but less than 100 yards over or under should never be used.