On War

by Carl von Clausewitz

The third form of defence—by a strong position taken up on the enemy’s side of the river—founds its efficacy on the danger in which it places the enemy of having his communications cut by the river, and being thus limited to some bridges. It follows, as a matter of course, that we are only speaking of great rivers with a great volume of water, as these alone can lead to such results, whilst a river which is merely in a deep ravine usually affords such a number of passages that all danger of the above disappears.

But the position of the defensive must be very strong, almost unassailable; otherwise he would just meet the enemy half way, and give up his advantages. But if it is of such strength that the enemy resolves not to attack it, he will, under certain circumstances, be confined thereby to the same bank with the defender. If the assailant crosses, he exposes his communications; but certainly, at the same time, he threatens ours. Here, as in all cases in which one army passes by another, the great point is, whose communications, by their number, situation, and other circumstances, are the best secured, and which has also, in other respects, most to lose, therefore can be outbid by his opponent; lastly, which possesses still in his army the most power of victory upon which he can depend in an extreme case. The influence of the river merely amounts to this, that it augments the danger of such a movement for both parties, as both are dependent on bridges. Now, in so far as we can assume that, according to the usual course of things, the passage of the defender, as well as of his depôts of all kinds, are better secured by fortresses than those of the offensive, in so far is such a defence conceivable, and one which might be substituted for the direct defence when circumstances are not favourable to that form. Certainly then the river is not defended by the army, nor the army by the river, but by the connection between the two the country is defended, which is the main point.

At the same time it must be granted that this mode of defence, without a decisive blow, and resembling the state of tension of two electric currents, of which the atmospheres only are as yet in contact, cannot stop any very powerful impulsive force. It might be applicable against even a great superiority of force on the side of the enemy, if their army is commanded by a cautious general, wanting in decision, and never disposed to push forward with energy; it might also answer when a kind of oscillation towards equality between the contending forces has previously arisen, and nothing but small advantages are looked for on either side. But if we have to deal with superior forces, led by a bold general, we are upon a dangerous course, very close to an abyss.

This form of defence looks so bold, and at the same time so scientific, that it might be called the elegant; but as elegance easily merges into folly, and as it is not so easily excused in war as in society, therefore we have had as yet few instances of this elegant art. From this third mode a special means of assistance for the first two forms is developed, that is, by the permanent occupation of a bridge and a tête du pont to keep up a constant threat of crossing.

Besides the object of an absolute defence with the main body, each of the three modes of defence may also have that of a feigned defence.

This show of a resistance, which it is not intended really to offer, is an act which is combined with many other measures, and fundamentally with every position which is anything more than a camp of route; but the feigned defence of a great river becomes a complete stratagem in this way, that it is necessary to adopt actually more or less a number of measures of detail, and that its action is usually on a greater scale and of longer duration than that of any other; for the act of passing a great river in sight of an army is always an important step for the assailant, one over which he often ponders long, or which he postpones to a more favourable moment.

For such a feigned defence it is therefore requisite that the main army should divide and post itself along the river, (much in the same manner as for a real defence); but as the intention of a mere demonstration shows that circumstances are not favourable enough for a real defence, therefore, from that measure as it always occasions a more or less extended and scattered disposition, the danger of serious loss may very easily arise if the corps should get engaged in a real resistance, even if not carried to an extremity; it would then be in the true sense a half measure. In a demonstration of defence, therefore, arrangement must be made for a sure concentration of the army at a point considerably (perhaps several days’ march) in rear, and the defence should not be carried beyond what is consistent with this arrangement.

In order to make our views plainer, and to show the importance of such a defensive demonstration, let us refer to the end of the campaign of 1813. Buonaparte repassed the Rhine with forty or fifty thousand men. To attempt to defend this river with such a force at all points where the Allies, according to the direction of their forces, might easily pass, that is, between Manheim and Nimeguen, would have been to attempt an impossibility. The only idea which Buonaparte could therefore entertain was to offer his first real resistance somewhere on the French Meuse, where he could make his appearance with his army in some measure reinforced. Had he at once withdrawn his forces to that point, the Allies would have followed close at his heels; had he placed his army in cantonments for rest behind the Rhine, the same thing must have taken place almost as soon, for at the least show of desponding caution on his part, the Allies would have sent over swarms of Cossacks and other light troops in pursuit, and, if that measure produced good results, other corps would have followed. The French corps had therefore nothing for it but to take steps to defend the Rhine in earnest. As Buonaparte could foresee that this defence must end in nothing whenever, the Allies seriously undertook to cross the river, it may therefore be regarded in the light of a mere demonstration, in which the French corps incurred hardly any danger, as their point of concentration lay on the Upper Moselle. Only Macdonald, who, as is known, was at Nimeguen with twenty thousand men, committed a mistake in deferring his retreat till fairly compelled to retire, for this delay prevented his joining Buonaparte before the battle of Brienne, as the retreat was not forced on him until after the arrival of Winzurgerode’s corps in January. This defensive demonstration on the Rhine, therefore, produced the result of checking the Allies in their advance, and induced them to postpone the crossing of the river until their reinforcements arrived, which did not take place for six weeks. These six weeks were of infinite value to Buonaparte. Without this defensive demonstration on the Rhine, Paris would have become the next immediate object after the victory of Leipsic, and it would have been impossible for the French to have given battle on that side of their capital.

In a river defence of the second class, therefore, in that of rivers of a smaller size, such demonstrations may also be used, but they will generally be less effectual, because mere attempts to cross are in such a case easier, and therefore the spell is sooner broken.

In the third kind of river defence, a demonstration would in all probability be still less effectual, and produce no more result than that of the occupation of any other temporary position.