On War

by Carl von Clausewitz

Its defect (the point on which the defender is very apt to err) is the over-extension of the defending force. It is so natural in such a case to be drawn on from one point of passage to another, and to miss the right point where we ought to stop; but then, if we do not succeed in fighting with the whole army united, we miss the intended effect; a defeat in battle, the necessity of retreat, confusion in many ways and losses reduce the army nearly to ruin, even although the resistance has not been pushed to an extremity.

In saying that the defensive, under the above conditions, should not extend his forces widely, that he should be in any case able to assemble all his forces on the evening of the day on which the enemy passes, enough is said, and it may stand in place of all combinations of time, power, and space, things which, in this case, must depend on many local points.

The battle to which these circumstances lead must have a special character—that of the greatest impetuosity on the side of the defender. The feigned passages by which the enemy will keep him for some time in uncertainty—will, in general prevent his discovering the real point of crossing a moment too soon. The peculiar advantages of the situation of the defender consist in the disadvantageous situation of the enemy’s corps just immediately in his front; if other corps, having passed at other points, menace his flank, he cannot, as in a defensive battle, counteract such movements by vigorous blows from his rear, for that would be to sacrifice the above-mentioned advantage of his situation; he must, therefore, decide the affair in his front before such other corps can arrive and become dangerous, that is, he must attack what he has before him as swiftly and vigorously as possible, and decide all by its defeat.

But the object of this form of river defence can never be the repulse of a very greatly superior force, as is conceivable in the direct defence of a large river; for as a rule we have really to deal with the bulk of the enemy’s force, and although we do so under favourable circumstances, still it is easy to see the relation between the forces must soon be felt.

This is the nature of the defence of rivers of a moderate size and deep valleys when the principal masses of the armies are concerned, for in respect to them the considerable resistance which can be offered on the ridges or scarps of the valley stands no comparison with the disadvantages of a scattered position, and to them a decisive victory is a matter of necessity. But if nothing more is wanted but the reinforcement of a secondary line of defence which is intended to hold out for a short time, and which can calculate on support, then certainly a direct defence of the scarps of the valley, or even of the river bank, may be made; and although the same advantages are not to be expected here as in mountain positions, still the resistance will always last longer than in an ordinary country. Only one circumstance makes this measure very dangerous, if not impossible: it is when the river has many windings and sharp turnings, which is just what is often the case when a river runs in a deep valley, Only look at the course of the Mosel. In a case of its defence, the corps in advance on the salients of the bends would almost inevitably be lost in the event of a retreat.

That a great river allows the same defensive means, the same form of defence, which we have pointed out as best suited for rivers of a moderate size, in connection with the mass of an army, and also under much more favourable circumstances, is plain of itself. It will come into use more especially when the point with the defender is to gain a decisive victory (Aspern).

The case of an army drawn up with its front close on a river, or stream, or deep valley, in order by that means to command a tactical obstacle to the approach to its position, or to strengthen its front, is quite a different one, the detailed examination of which belongs to tactics. Of the effect of this we shall only say this much, that it is founded on a delusion.—If the cleft in the ground is very considerable, the front of the position becomes absolutely unassailable. Now, as there is no more difficulty in passing round such a position than any other, it is just the same as if the defender had himself gone out of the way of the assailant, yet that could hardly be the object of the position. A position of this kind can, therefore, only be advisable when, as a consequence of its position, it threatens the communications of the assailant, so that every deviation by him from the direct road is fraught with consequences altogether too serious to be risked.

In this second form of defence, feigned passages are much more dangerous, for the assailant can make them more easily, while, on the other hand, the proposition for the defender is, to assemble his whole army at the right point. But the defender is certainly not quite so much limited for time here, because the advantage of his situation lasts until the assailant has massed his whole force, and made himself master of several crossings; moreover, also, the simulated attack has not the same degree of effect here as in the defence of a cordon, where all must be held, and where, therefore, in the application of the reserve, it is not merely a question, as in our proposition, where the enemy has his principal force, but the much more difficult one, Which is the point he will first seek to force?

With respect to both forms of defence of large and small rivers, we must observe generally, that if they are undertaken in the haste and confusion of a retreat, without preparation, without the removal of all means of passage, and without an exact knowledge of the country, they cannot certainly fulfil what has been here supposed; in most such cases, nothing of the kind is to be calculated upon; and therefore it will be always a great error for an army to divide itself over extended positions.

As everything usually miscarries in war, if it is not done upon clear convictions and with the whole will and energy, so a river defence will generally end badly when it is only resorted to because we have not the heart to meet the enemy in the open field, and hope that the broad river or the deep valley will stop him. When that is the case, there is so little confidence in the actual situation that both the general and his army are usually filled with anxious forebodings, which are almost sure to be realized quick enough. A battle in the open field does not suppose a perfectly equal state of circumstances beforehand, like a duel; and the defender who does not know how to gain for himself any advantages, either through the special nature of the defence, through rapid marches, or by knowledge of the country and freedom of movement, is one whom nothing can save, and least of all will a river or its valley be able to help him.