Front Page Titles (by Subject) CHAPTER XIII: STRONG POSITIONS AND ENTRENCHED CAMPS - On War, vol. 2
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CHAPTER XIII: STRONG POSITIONS AND ENTRENCHED CAMPS - Carl von Clausewitz, On War, vol. 2 
On War, trans. Col. J.J. Graham. New and Revised edition with Introduction and Notes by Col. F.N. Maude, in Three Volumes (London: Kegan Paul, Trench, Trubner & C., 1918). Vol. 2.
Part of: On War
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STRONG POSITIONS AND ENTRENCHED CAMPS
We have said in the preceding chapter that a position so strong through nature, assisted by art, that it is unassailable, does not come under the meaning of an advantageous field of battle, but belongs to a peculiar class of things. We shall in this chapter take a review of what constitutes the nature of this peculiarity, and on account of the analogy between such positions and fortresses, call them strong positions.
Merely by entrenchments alone they can hardly be made, except as entrenched camps resting on fortresses; but still less are they to be found ready formed entirely by natural obstacles. Art usually lends a hand to assist nature, and therefore they are frequently designated as entrenched camps or positions. At the same time, that term may really be applied to any position strengthened more or less by field works, which need have nothing in common with the nature of the position we are now considering.
The object of a strong position is to make the force there stationed in point of fact unattackable, and by that means, either really to cover a certain space directly, or only the troops which occupy that space in order then, through them, in another way to effect the covering of the country indirectly. The first was the signification of the lines of former times, for instance, those on the French frontier; the latter, is that of entrenched camps laid out near fortresses, and showing a front in every direction.
If, for instance, the front of a position is so strong by works and hindrances to approach that an attack is impossible, then the enemy is compelled to turn it, to make his attack on a side of it or in rear. Now to prevent this being easily done, points d’appui were sought for these lines, which should give them a certain degree of support on the flanks, such as the Rhine and the Vosges give the lines in Alsace. The longer the front of such a line the more easily it can be protected from being turned, because every movement to turn it is attended with danger to the side attempting the movement, the danger increasing in proportion as the required movement causes a greater deviation from the normal direction of the attacking force. Therefore, a considerable length of front, which can be made unassailable, and good flank-supports, ensure the possibility of protecting a large space of territory directly from hostile invasion: at least, that was the view in which works of this class originated; that was the object of the lines in Alsace, with their right flank on the Rhine and the left on the Vosges; and the lines in Flanders seventy-five miles long, resting their right on the Scheldt and the fortress of Tournay, their left on the sea.
But when we have not the advantages of such a long well-defended front, and good flank-supports, if the country is to be held generally by a force well entrenched, then that force (and its position) must be protected against being turned by such an arrangement that it can show a front in every direction. But then the idea of a thoroughly covered tract of country vanishes, for such a position is only strategically a point which covers the force occupying it, and thus secures to that force the power of keeping the field, that is to say, maintaining itself in the country. Such a camp cannot be turned, that is, cannot be attacked in flank or rear by reason of those parts being weaker than its front, for it can show front in all directions, and is equally strong everywhere. But such a camp can be passed by, and that much easier than a fortified line, because its extent amounts to nothing.
Entrenched camps connected with fortresses are in reality of this second kind, for the object of them is to protect the troops assembled in them; but their further strategic meaning, that is, the application of this protected force, is somewhat different from that of other fortified camps.
Having given this explanation of the origin of these three different defensive means, we shall now proceed to consider the value of each of them separately, under the heads of strong lines, strong positions, and entrenched camps resting on fortresses.
1. Lines.—These lead to the worst kind of cordon war: the obstacle which they present to the aggressor is of no value at all unless they are defended by a powerful fire; in themselves they are simply worthless. But now the extent to which an Army can furnish an effective fire is generally very small in proportion to the extent of country to be defended; the lines can, therefore, only be short, and consequently cover only a small extent of country, or the Army will not be able really to defend the lines at all points. In consequence of this, the idea was started of not occupying all points in the line, but only watching them, and defending them by means of strong reserves, in the same way as a small river may be defended; but this procedure is in opposition to the nature of the means. If the natural obstacles of the ground are so great that such a method of defence could be applied, then the entrenchments were needless, and entail danger, for that method of defence is not local, and entrenchments are only suited to a strictly local defence; but if the entrenchments themselves are to be considered the chief impediments to approach, then we may easily conceive that an undefended line will not have much to say as an obstacle to approach. What is a twelve or fifteen feet ditch, and a rampart ten or twelve feet high, against the united efforts of many thousands, if these efforts are not hindered by the fire of an enemy? The consequence, therefore, is, that if such lines are short and tolerably well defended by troops, they can be turned; but if they are extensive, and not sufficiently occupied, they can be attacked in front, and taken without much difficulty.
Now as lines of this description tie the troops down to a local defence, and take away from them all mobility, they are a bad and senseless means to use against an enterprising enemy. If we find them long retained in modern Wars in spite of these objections, the cause lies entirely in the low degree of energy impressed on the conduct of War, one consequence of which was, that seeming difficulties often effected quite as much as real ones. Besides, in most campaigns these lines were used merely for a secondary defence against irregular incursions; if they have been found not wholly inefficacious for that purpose, we must only keep in view, at the same time, how much more usefully the troops required for their defence might have been employed at other points. In the latest Wars such lines have been out of the question, nowhere do we find any trace of them; and it is doubtful if they will ever reappear.1
2. Positions.—The defence of a tract of country continues (as we shall show more plainly in the 27th chapter) as long as the force designated for it maintains itself there, and only ceases if that force removes and abandons it.
If a force is to maintain itself in any district of country which is attacked by very superior forces, the means of protecting this force against the power of the sword by a position which is unassailable is a first consideration.
Now such a position, as before said, must be able to show a front in all directions; and in conformity with the usual extent of tactical positions, if the force is not very large (and a large force would be contrary to the nature of the supposed case) it would take up a very small space, which, in the course of the combat, would be exposed to so many disadvantages that, even if strengthened in every possible way by entrenchments, we could hardly expect to make a successful defence. Such a camp, showing front in every direction, must therefore necessarily have an extent of sides proportionably great; but these sides must likewise be as good as unassailable; to give this requisite strength, notwithstanding the required extension, is not within the compass of the art of field fortification; it is therefore a fundamental condition that such a camp must derive part of its strength from natural impediments of ground which render many places impassable and others difficult to pass. In order, therefore, to be able to apply this defensive means, it is necessary to find such a spot, and when that is wanting, the object cannot be attained merely by field works. These considerations relate more immediately to tactical results in order that we may first establish the existence of this strategic means; we mention as examples for illustration, Pirna, Bunzelwitz, Colberg, Torres Vedras, and Drissa.
Now, as respects the strategic properties and effects. The first condition is naturally that the force which occupies this camp shall have its subsistence secured for some time, that is, for as long as we think the camp will be required, and this is only possible when the position has behind it a port, like Colberg and Torres Vedras, or stands in connection with a fortress like Bunzelwitz and Pirna, or has large depôts within itself or in the immediate vicinity, like Drissa.
It is only in the first case that the provisioning can be ensured for any time we please; in the second and third cases, it can only be so for a more or less limited time, so that in this point there is always danger. From this appears how the difficulty of subsistence debars the use of many strong points which otherwise would be suitable for entrenched positions, and, therefore, makes those that are eligible scarce.
In order to ascertain the eligibility of a position of this description, its advantages and defects, we must ask ourselves what the aggressor can do against it.
a. The assailant can pass by this strong position, pursue his enterprise, and watch the position with a greater or less force.
We must here make a distinction between the cases of a position which is occupied by the main body, and one only occupied by an inferior force.
In the first case the passing by the position can only benefit the assailant, if, besides the principal force of the defendant, there is also some other attainable and decisive object of attack, as, for instance, the capture of a fortress or a capital city, &c. But even if there is such an object, he can only follow it if the strength of his base and the direction of his lines of communication are such that he has no cause to fear operations against his strategic flanks.
The conclusions to be drawn from this with respect to the admissibility and eligibility of a strong position for the main body of the defender’s Army are, that it is only an advisable position when either the possibility of operating against the strategic flank of the aggressor is so decisive that we may be sure beforehand of being able in that way to keep him at a point where his Army can effect nothing, or in a case where there is no object attainable by the aggressor for which the defence need be uneasy. If there is such an object, and the strategic flank of the assailant cannot be seriously menaced, then such position should not be taken up, or if it is it should only be as a feint to see whether the assailant can be imposed upon respecting its value; this is always attended with the danger, in case of failure, of being too late to reach the point which is threatened.
If the strong position is only held by an inferior force, then the aggressor can never be at a loss for a further object of attack, because he has it in the main body itself of the enemy’s Army; in this case, therefore, the value of the position is entirely limited to the means which it affords of operating against the enemy’s strategic flank, and depends upon that condition.
b. If the assailant does not venture to pass by a position, he can invest it and reduce it by famine. But this supposes two conditions beforehand: first, that the position is not open in rear, and secondly, that the assailant is sufficiently strong to be able to make such an investment. If these two conditions are united then the assailant’s Army certainly would be neutralised for a time by this strong position, but at the same time, the defensive pays the price of this advantage by a loss of his defensive force.
From this, therefore, we deduce that the occupation of such a strong position with the main body is a measure only to be taken,—
aa. When the rear is perfectly safe (Torres Vedras).
bb. When we foresee that the enemy’s force is not strong enough formally to invest us in our camp. Should the enemy attempt the investment with insufficient means, then we should be able to sally out of the camp and beat him in detail.
cc. When we can count upon relief like the Saxons at Pirna, 1756, and as took place in the main at Prague, because Prague could only be regarded as an entrenched camp in which Prince Charles would not have allowed himself to be shut up if he had not known that the Moravian army could liberate him.
One of these three conditions is therefore absolutely necessary to justify the choice of a strong position for the main body of an Army; at the same time we must add that the two last are bordering on a great danger for the defensive.
But if it is a question of exposing an inferior corps to the risk of being sacrificed for the benefit of the whole, then these conditions disappear, and the only point to decide is whether by such a sacrifice a greater evil may be avoided. This will seldom happen; at the same time it is certainly not inconceivable. The entrenched camp at Pirna prevented Frederick the Great from attacking Bohemia, as he would have done, in the year 1756. The Austrians were at that time so little prepared, that the loss of that kingdom appears beyond doubt; and perhaps, a greater loss of men would have been connected with it than the 17,000 allied troops who capitulated in the Pirna camp.
c. If none of those possibilities specified under a and b are in favour of the aggressor; if, therefore, the conditions which we have there laid down for the defensive are fulfilled, then there remains certainly nothing to be done by the assailant but to fix himself before the position, like a setter before a covey of birds, to spread himself, perhaps, as much as possible by detachments over the country, and contenting himself with these small and indecisive advantages to leave the real decision as to the possession of territory to the future. In this case the position has fulfilled its object.
3. Entrenched camps near fortresses.—They belong, as already said, to the class of entrenched positions generally, in so far, as they have for their object to cover not a tract of territory, but an armed force against a hostile attack, and only differ in reality from the other in this, that with the fortress they make up an inseparable whole, by which they naturally acquire much greater strength.
But there follows further from the above the undermentioned special points.
a. That they may also have the particular object of rendering the siege of the fortress either impossible or extremely difficult. This object may be worth a great sacrifice of troops if the place is a port which cannot be blockaded, but in any other case we have to take care lest the place is one which may be reduced by hunger so soon that the sacrifice of any considerable number of troops is not justifiable.
b. Entrenched camps can be formed near fortresses for smaller bodies of troops than those in the open field. Four or five thousand men may be invincible under the walls of a fortress, when, on the contrary, in the strongest camp in the world, formed in the open field, they would be lost.
c. They may be used for the assembly and organisation of forces which have still too little solidity to be trusted in contact with the enemy, without the support afforded by the works of the place, as for example, recruits, militia, national levies, &c.
They might, therefore, be recommended as a very useful measure, in many ways, if they had not the immense disadvantage of injuring the fortress, more or less, when they cannot be occupied; and to provide the fortress always with a garrison, in some measure sufficient to occupy the camp also, would be much too onerous a condition.
We are, therefore, very much inclined to consider them only advisable for places on a sea coast, and as more injurious than useful in all other cases.
If, in conclusion, we should summarise our opinion in a general view, then strong and entrenched positions are—
1. The more requisite the smaller the country, the less the space afforded for a retreat.
2. The less dangerous the more surely we can reckon on succouring or relieving them by other forces, or by the inclemency of season, or by a rising of the nation, or by want, &c.
3. The more efficacious, the weaker the elementary force of the enemy’s attack.
[1 ]They did reappear, however, in the Civil War in America, in Bulgaria, in South Africa and in Manchuria.