When the main guard comes up, in the case where the vanguard is checked, the section commander should take the earliest opportunity of placing himself under the battery commander, and at this stage the guns should be used to seize and hold positions of importance, especially artillery positions. If the advanced-guard action discloses the fact that the main body of the enemy has been encountered, and the G.O.C decides to engage, the advanced guard will be required to seize all positions of tactical value and to hold off the enemy until the main body has had time to arrive and deploy. Their action will vary according to whether the G.O.C. decides to act on the offensive or defensive. The latest German Regulations say: “On becoming engaged, that side will have the advantage which gains the start over its opponents in readiness for action, and thus reaps the benefit of the initiative.” No arm is better able to assist in this than the machine gun, and every available battery should be brought up at this stage to take part in the advanced-guard engagement. The Germans say: “The advanced guard will fight on a wider front than that ordinarily allotted to a force of its size, so as to seriously engage the enemy. It will be disposed in groups more or less detached, which will occupy those positions the possession of which will most protect the deployment of the main body. _It will be assisted by detachments of machine guns, which will be placed for preference on those positions which it is most necessary to prevent the enemy from capturing._”[16] The commander of the machine guns of the advanced guard is under the immediate orders of the O.C. advanced guard, and must co-operate with him throughout the engagement. All officers with machine guns must remember that isolated action is useless, and that however effective their fire may be locally, unless it directly furthers the object of the action, it is an unjustifiable waste of fire power. The seizure of ground likely to be of use to the main body--particularly artillery positions--must be the first consideration of machine guns with the advanced-guard infantry, once the infantry are in action. That they can hold these unsupported is certain. “There never has been and cannot be such a thing as a successful attack on a line of machine guns in a favourable position in action, until the machine guns have been well battered by artillery fire,” says Lieutenant Parker in his book _Tactical Organisation and Uses of Machine Guns in the Field_.