On War

by Carl von Clausewitz

With respect to the strength of an advanced guard we have little to say, as now very properly it is the general custom to detail for that duty one or more component parts of the army of the first class, reinforced by part of the cavalry: so that it consists of a corps, if the army is formed in corps; of a division, if the organisation is in divisions.

It is easy to perceive that in this respect also the great number of higher members or divisions is an advantage.

How far the advanced guard should be pushed to the front must entirely depend on circumstances; there are cases in which it may be more than a day’s march in advance, and others in which it should be immediately before the front of the army. If we find that in most cases between one and three miles is the distance chosen, that shows certainly that circumstances have usually pointed out this distance as the best; but we cannot make of it a rule by which we are to be always guided.

In the foregoing observations we have lost sight altogether of outposts, and therefore we must now return to them again.

In saying, at the commencement, that the relations between outposts and stationary troops is similar to that between advanced guards and troops in motion, our object was to refer the conceptions back to their origin, and keep them distinct in future; but it is clear that if we confine ourselves strictly to the words we should get little more than a pedantic distinction.

If an army on the march halts at night to resume the march next morning, the advanced guard must naturally do the same, and always organise the outpost duty, required both for its own security and that of the main body, without on that account being changed from an advanced guard into a line of outposts. To satisfy the notion of that transformation, the advanced guard would have to be completely broken up into a chain of small posts, having either only a very small force, or none at all in a form approaching to a mass. In other words, the idea of a line of outposts must predominate over that of a concentrated corps.

The shorter the time of rest of the army, the less complete does the covering of the army require to be, for the enemy has hardly time to learn from day to day what is covered and what is not. The longer the halt is to be the more complete must be the observation and covering of all points of approach. As a rule, therefore, when the halt is long, the vanguard becomes always more and more extended into a line of posts. Whether the change becomes complete, or whether the idea of a concentrated corps shall continue uppermost, depends chiefly on two circumstances. The first is the proximity of the contending armies, the second is the nature of the country.

If the armies are very close in comparison to the width of their front, then it will often be impossible to post a vanguard between them, and the armies are obliged to place their dependence on a chain of outposts.

A concentrated corps, as it covers the approaches to the army less directly, generally requires more time and space to act efficiently; and therefore, if the army covers a great extent of front, as in cantonments, and a corps standing in mass is to cover all the avenues of approach, it is necessary that we should be at a considerable distance from the enemy; on this account winter quarters, for instance, are generally covered by a cordon of posts.

The second circumstance is the nature of the country; where, for example, any formidable obstacle of ground affords the means of forming a strong line of posts with but few troops, we should not neglect to take advantage of it.