service of protection must be performed as far as possible by the manner in which the army advances, that is, eo ipso by the army itself. If a force must be specially detailed for this duty, and therefore a partition of forces is required, this cannot but naturally weaken the force of the blow itself.—As a large army is always in the habit of advancing with a front of a day’s march at least in breadth, therefore, if the lines of retreat and communication do not deviate much from the perpendicular, the covering of those lines is in most cases attained by the front of the army.
Dangers of this description, to which the assailant is exposed, must be measured chiefly by the situation and character of the adversary. When everything lies under the pressure of an imminent great decision, there is little room for the defender to engage in undertakings of this description; the assailant has, therefore, in ordinary circumstances not much to fear. But if the advance is over, if the assailant himself is gradually passing into the defensive, then the covering of the rear becomes every moment more necessary, becomes more a thing of the first importance. For the rear of the assailant being naturally weaker than that of the defender, therefore the latter, long before he passes over to the real offensive, and even at the same time that he is yielding ground, may have commenced to operate against the communications of the assailant.