On War

by Carl von Clausewitz

The crests of the higher Alps in particular are so difficult of access, and afford so little space for the accommodation of troops, that it would be impossible to place any considerable bodies of men there. Now if we must positively have armies in mountains to keep possession of them, there is nothing to be done but to place them in the valleys. At first sight this appears erroneous, because, in accordance with the prevalent theoretical ideas, it will be said, the heights command the valleys. But that is really not the case. Mountain ridges are only accessible by a few paths and rude tracks, with a few exceptions only passable for infantry, whilst the carriage roads are in the valleys. The enemy can only appear there at certain points with infantry; but in these mountain masses the distances are too great for any effective fire of small arms, and therefore a position in the valleys is less dangerous than it appears. At the same time, the valley defence is exposed to another great danger, that of being cut off. The enemy can, it is true, only descend into the valley with infantry, at certain points, slowly and with great exertion; he cannot, therefore, take us by surprise; but none of the positions we have in the valley defend the outlets of such paths into the valley. The enemy can, therefore, bring down large masses gradually, then spread out, and burst through the thin and from that moment weak line, which, perhaps, has nothing more for its protection than the rocky bed of a shallow mountain-stream. But now retreat, which must always be made piecemeal in a valley, until the outlet from the mountains is reached, is impossible for many parts of the line of troops; and that was the reason that the Austrians in Switzerland almost always lost a third, or a half of their troops taken prisoners.—

Now a few words on the usual way of dividing troops in such a method of defence.

Each of the subordinate positions is in relation with a position taken up by the principal body of troops, more or less in the centre of the whole line, on the principal road of approach. From this central position, other corps are detached right and left to occupy the most important points of approach, and thus the whole is disposed in a line, as it were, of three, four, five, six posts, &c. How far this fractioning and extension of the line shall be carried, must depend on the requirements of each individual case. An extent of a couple of marches, that is, six to eight miles is of moderate length, and we have seen it carried as far as twenty or thirty miles.

Between each of these separate posts, which are one or two leagues from each other, there will probably be some approaches of inferior importance, to which afterwards attention must be directed. Some very good posts for a couple of battalions each are selected, which form a good connection between the chief posts, and they are occupied. It is easy to see that the distribution of the force may be carried still further, and go down to posts occupied only by single companies and squadrons; and this has often happened. There are, therefore, in this no general limits to the extent of fractioning. On the other hand, the strength of each post must depend on the strength of the whole; and therefore we can say nothing as to the possible or natural degree which should be observed with regard to the strength of the principal posts. We shall only append, as a guide, some maxims which are drawn from experience and the nature of the case.

1. The more lofty and inaccessible the mountains are, so much the further this separation of divisions of the force not only may be, but also must be, carried; for the less any portion of a country can be kept secure by combinations dependent on the movement of troops, so much the more must the security be obtained by direct covering. The defence of the Alps requires a much greater division of force, and therefore approaches nearer to the cordon system, than the defence of the Vosges or the Giant mountains.

2. Hitherto, wherever defence of mountains has taken place, such a division of the force employed has been made that the chief posts have generally consisted of only one line of infantry, and in a second line, some squadrons of cavalry; at all events, only the chief post established in the centre has perhaps had some battalions in a second line.

3. A strategic reserve, to reinforce any point attacked, has very seldom been kept in rear, because the extension of front made the line feel too weak already in all parts. On this account the support which a post attacked has received, has generally been furnished from other posts in the line not themselves attacked.

4. Even when the division of the forces has been relatively moderate, and the strength of each single post considerable, the principal resistance has been always confined to a local defence; and if once the enemy succeeded in wresting a post, it has been impossible to recover it by any supports afterwards arriving.

How much, according to this, may be expected from mountain defence, in what cases this means may be used, how far we can and may go in the extension and fractioning of the forces—these are all questions which theory must leave to the tact of the general. It is enough if it tells him what these means really are, and what rôle they can perform in the active operations of the army.

A general who allows himself to be beaten in an extended mountain position deserves to be brought before a court martial.