Certain points must be noted about the positions chosen for these successive fire-fights, and the choice of the positions is so difficult that an experienced staff officer should be specially detailed for the work, Positions chosen must be in the enemy's way and the lines of withdrawal to them must not converge; they must be easy to defend and difficult to attack; the flanks must be secure from direct attack and effective enfilade fire, necessitating a wide detour (and consequent gain of time from the enemy) before they can be threatened; long-range artillery fire on the lines of approach should be possible in order to delay and break up the enemy's advance; and each position chosen for the next line of resistance should be unseen by the {123} pursuing enemy, and sufficiently far away from the line last occupied to induce him to resume his march formation. This will necessitate a repetition on the part of the enemy of all the stages of the attack--the discovery and the report on the position, the decision to attack, and the deployment into attack formation. It will often be of advantage for a Rear Guard to take up a delaying position one or two hours before dark, as the enemy will then have to attack with darkness approaching and may wish to defer the attack until daylight, thus gaining several hours for the protected force. "The first position taken up by a Rear Guard after an unsuccessful fight must be held longer, as a rule, than the subsequent positions, because when once the defeated army has got well away along the roads and has regained some semblance of organisation, the march continues without interruption unless some obstacle has to be crossed" (General Haking, "Staff Rides"). It can also be noted that as it is seldom the intention of the Rear Guard commander to deliver a decisive counter-attack, he can detail a very large proportion of his force to hold the successive positions, with local reserves, for purely local counter-attacks; and for the same reason, an obstacle in front of his position (which would make that position unsuitable for the Active Defence, as it would prevent the advance of the General Reserve to the decisive counter-attack) is most welcome in the Delaying Action of a Rear Guard fighting for time for its Main Body. When at length a line of resistance is evacuated, the heavy artillery will be withdrawn first to move to a distant fire position, then the slow moving infantry and the light artillery (under the protective fire of the aircraft and mobile troops), and last the cavalry and other mobile troops, who by reason of their superior mobility, can hang on to the last and can protect the flanks of the Rear Guard as they fall back, before {124} resuming their work as a Rear Party, observing and resisting the advanced troops of the pursuing force.