Generally speaking, there are two kinds of machine gun tactics; the tactics of long range, rendered possible by the conditions of the en trenchment battle, and the tactics of medium and short ranges, which have their place in the manceuver battle in the open, and the assault during the entrenchment battle. Long range fire is rendered practicable and effective in the entrenchment battle by the fact that the enemy's position is fixed and easily defined. Systematic aerial reconnaissance renders it possible to map out most accurately the position of the advanced trenches which form the enemy's firing line, the trenches farther back, where he keeps his sup ports and reserves, and the lines by which these supports and all supplies of ammunition must be brought tip to the advanced trench. Recon naissance of the enemy's position can reveal the areas where it is vulnerable to machine gun fire, and this fire can be directed on these areas with certainty. Thus the fire from the guns harass the enemy, impede his movements and inflict loss upon him.
It is obvious that the longer the range the more chance there is of selecting lines of trench that arc open to enfilade. The machine gunner can pick out lines of trench far to the right or left, on which he can bring diagonal indirect fire. The beaten zone is so moderate in extent that several guns have to be used to gether to sweep a given extent of ground either in frontage or depth, though the single section of two or four guns is sufficient when firing on a narrow target, such as a communication trench.
Machine guns effectually cover the reorgan ization or retirement of the infantry they are supporting. Some guns are used to create a screen of fire between the infantry and the enemy; others use high angle fire against the reserves which the enemy is bringing up for the counter attack. In a prolonged retirement a
rear guard should be with machine guns. The approved plan is to divide the machine gun force into two portions, one of which is in action while the other is taking up a second position farther to the rear.
In the case of cavalry against cavalry, the action of machine guns is analogous to that of horse artillery. They must endeavor to take up a flank position, from which they can bring their fire to bear upon the enemy's cavalry while their own cavalry is advancing to the attack. The guns have to provide for their own pro tection, and be able to take up a position where they are practically safe from mounted attacks. Armored cars have provided a new field for machine guns. As a rule the heavier type of i car, in which the gun is permanently mounted in a kind of turret, operates on the roads. It gives invaluable support to patrols and detached parties, the men working the gun being them selves fairly safe from rifle and machine gun fire. The drawback of the car is that it is rather a prominent target for artillery. In an other type the gun is merely carried up by the car and is then taken out and placed in position.
Motor machine guns are successfully used to close a gap in a line or support troops who arc rapidly driven in. In covering a retreat along a good road, they are invaluable. Their normal work, however, is to support patrols and ad vanced parties, and to operate against enemy patrols. To sum up, (1) machine gun fire should be used liberally to save the infantry, (2) it should he used from flanking positions, (3) the machine guns should he concealed in order that their fire may come as a surprise, and (4) they should he echeloned in depth and sheltered to prevent their being destroyed early in the action.