If a position affording concealment is not available, one should be selected which from the nature of its background will be difficult for the enemy to locate. As the opportunities for the effective action of machine guns will often be very brief, and as the guns will usually be employed singly, the non-commissioned officer in charge of each gun will, as a rule, have to act on his own initiative in choosing the objective, judging the range, and in deciding when to open fire. As a general rule, machine guns are best adapted for action at effective ranges; at these it is usually possible to distinguish the target, to ascertain its range, and to observe the effects of the fire. When, however, concealment and protection from fire exist, it may sometimes be advisable to bring machine guns into action at decisive range. If a sufficiently large target be offered and the range be known, the concentration and rapidity of their fire will enable guns to be employed, with considerable effect, at long ranges. Machine guns should seldom engage artillery at long rifle range, for in such circumstances superiority of fire will always rest with the latter if the machines are located. Within effective range, however, machine guns, if concealed, should inflict considerable loss on hostile artillery. Engagements with their lines of skirmishers should be avoided, for the risk of disclosing the position of the guns and the heavy expenditure of ammunition involved will rarely be justified by results. Since the gun is not well adapted for keeping up protracted fire, it may be often expedient to withdraw it from action, move it elsewhere, or hold it in reserve for a more favourable opportunity. The selection of a target upon which to fire should be governed by (_a_) its tactical importance; (_b_) its dimensions and vulnerability. It is essential that due regard to economy of ammunition should be observed. When, however, it is decided to open fire, the ammunition necessary to secure the results sought must be expended without hesitation. “Deliberate fire” will rarely be resorted to. In cases where a favourable target is offered, prolonged “rapid fire” may be employed, but the most suitable description of fire will usually be “rapid” in series of from 25 to 30 rounds.