With reference to corps placed on the sides or flanks, the object of which we have before explained, the mode of action is in most cases more or less connected with circumstances which belong to the province of immediate application. The simplest way is to look upon them as advanced guards placed on the sides, which being at the same time thrown out somewhat in advance, retreat in an oblique direction upon the army.
As these corps are not immediately in the front of the army, and cannot be so easily supported as a regular advanced guard, they would, therefore, be exposed to greater danger if it was not that the enemy’s offensive power in most cases is somewhat less at the outer extremities of his line, and in the worst cases such corps have sufficient room to give way without exposing the army so directly to danger as a flying advanced guard would in its rapid retreat.
The most usual and best means of supporting an advanced corps is by a considerable body of cavalry, for which reason, when necessary from the distance at which the corps is advanced, the reserve cavalry is posted between the main body and the advanced corps.
The conclusion to be drawn from the preceding reflections is, that an advanced corps effects more by its presence than by its efforts, less by the combats in which it engages than by the possibility of those in which it might engage: that it should never attempt to stop the enemy’s movements, but only serve like a pendulum to moderate and regulate them, so that they may be made matter of calculation.