On War

by Carl von Clausewitz

The following are the purposes for which such a corps may be used, and therefore those which determine its duties in practice.

1. To insure a stouter resistance, and make the enemy advance with more caution; consequently to do the duties of a van-guard on a greater scale, whenever our arrangements are such as to require time before they can be carried into effect.

2. If the central mass of the army is very large, to be able to keep this unwieldy body at some distance from the enemy, while we still remain close to him with a more moveable body of troops.

3. That we may have a corps of observation close to the enemy, if there are any other reasons which require us to keep the principal mass of the army at a considerable distance.

The idea that weaker look-out posts, mere partisan corps, might answer just as well for this observation is set aside at once if we reflect how easily a weak corps might be dispersed, and how very limited also are its means of observation as compared with those of a considerable corps.

4. In the pursuit of the enemy. A single corps as advanced guard, with the greater part of the cavalry attached to it, can move quicker, arriving later at its bivouac, and moving earlier in the morning than the whole mass.

5. Lastly, on a retreat, as rearguard, to be used in defending the principal natural obstacles of ground. In this respect also the centre is exceedingly important. At first sight it certainly appears as if such a rearguard would be constantly in danger of having its flanks turned. But we must remember that, even if the enemy succeeds in overlapping the flanks to some extent, he has still to march the whole way from there to the centre before he can seriously threaten the central mass, which gives time to the rearguard of the centre to prolong its resistance, and remain in rear somewhat longer. On the other hand, the situation becomes at once critical if the centre falls back quicker than the wings; there is immediately an appearance as if the line had been broken through, and even the very idea or appearance of that is to be dreaded. At no time is there a greater necessity for concentration and holding together, and at no time is this more sensibly felt by every one than on a retreat. The intention always is, that the wings in case of extremity should close upon the centre; and if, on account of subsistence and roads, the retreat has to be made on a considerable width (of country), still the movement generally ends by a concentration on the centre. If we add to these considerations also this one, that the enemy usually advances with his principal force in the centre and with the greatest energy against the centre, we must perceive that the rear guard of the centre is of special importance.

Accordingly, therefore, a special corps should always be thrown forward as an advanced guard in every case where one of the above relations occurs. These relations almost fall to the ground if the centre is not stronger than the wings, as, for example, Macdonald when he advanced against Blücher, in Silesia, in 1813, and the latter, when he made his movement towards the Elbe. Both of them had three corps, which usually moved in three columns by different roads, the heads of the columns in line. On this account no mention is made of their having had advanced guards.

But this disposition in three columns of equal strength is one which is by no means to be recommended, partly on that account, and also because the division of a whole army into three parts makes it very unmanageable, as stated in the fifth chapter of the third book.

When the whole is formed into a centre with two wings separate from it, which we have represented in the preceding chapter as the most natural formation as long as there is no particular object for any other, the corps forming the advanced guard, according to the simplest notion of the case, will have its place in front of the centre, and therefore before the line which forms the front of the wings; but as the first object of corps thrown out on the flanks is to perform the same office for the sides as the advanced guard for the front, it will very often happen that these corps will be in line with the advanced guard, or even still further thrown forward, according to circumstances.