[555]. Machine guns in attack; fire of position. In attack, if fire of position is practicable, they are of great value. In this case fire should not be opened by the machine guns until the attack is well advanced. At a critical period in the attack, such fire, if suddenly and unexpectedly opened, will greatly assist the advancing line. The fire must be as heavy as possible and must be continued until masked by friendly troops or until the hostile artillery finds the machine guns. (541)
[556]. Machine guns in defense. In the defense, machine guns should be used in the same general manner as described above for the attack. Concealment and patient waiting for critical moments and exceptional opportunities are the special characteristics of the machine-gun service in decisive actions. (542)
[557]. Machine guns as part of reserve; use in covering withdrawal. As part of the reserve, machine guns have special importance. If they are with the troops told off to protect the flanks, and if they are well placed, they will often produce decisive results against a hostile turning movement. They are especially qualified to cover a withdrawal or make a captured position secure. (543)
[558]. Machine guns not to form part of firing line of attack. Machine guns should not be assigned to the firing line of an attack. They should be so placed that fire directed upon them is not likely to fall upon the firing line. (544)
[559]. Effectiveness of machine guns against skirmish line, except when lying down or crawling. A skirmish line can not advance by walking or running when hostile machine guns have the correct range and are ready to fire. Machine-gun fire is not specially effective against troops lying on the ground or crawling. (545)
[560]. Silencing of machine guns by infantry. When opposed by machine guns without artillery to destroy them, infantry itself must silence them before it can advance.
An infantry command that must depend upon itself for protection against machine guns should concentrate a large number of rifles on each gun in turn and until it has silenced it. (546)
In addition to the above, which the Infantry Drill Regulations gives on the subject of machine guns, the following, based on the use of machine guns in the European War, is given:
[561]. Machine guns essentially automatic rifles. They are essentially automatic rifles, designed to fire the ordinary rifle cartridge and capable of delivering a stream of small bullets at a rate of as high as 600 per minute. Experience in the European war has determined that the rate of 400 shots per minute is the desirable maximum. Their ranges are the same as for the rifle. The fire of a machine gun has been estimated as equal to that of 30 men.
[562]. Mounts. Machine guns are usually mounted on tripods or wheels. The weight of certain types is such that they can readily be carried by the soldier from one point to another.