Front Page Titles (by Subject) 3.—: PRINCIPLES FOR THE USE OF GROUND - On War, vol. 3
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3.—: PRINCIPLES FOR THE USE OF GROUND - Carl von Clausewitz, On War, vol. 3 
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. 3.
Part of: On War
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PRINCIPLES FOR THE USE OF GROUND
(1) The terrain (the ground or country) gives two advantages in War.
The first is, that obstacles to approach are thus presented which either render it impossible for an enemy to reach certain points, or compel him to march slowly to keep in column, &c.
The second is, that obstacles of ground enable us to conceal the position of our troops.
Both advantages are very important, but the second appears to me the greatest: at all events it is certainly the one which we can most frequently make use of, because, even the most level country, in most cases, still allows of drawing up troops more or less under cover.
Formerly, the first of these advantages was almost the only one known, and very little use was made of the second. Now the mobility of all Armies is such, that the first is of less service, and just on that account we must make use the more frequently of the second. The first of these two advantages is only serviceable in the defensive, the second, in both attack and defence.
(2) The ground, considered as an obstacle to approach, is of use chiefly in the following points: (a) as a support for the flanks, (b) as a means of strengthening the front.
(3) As a fit support for a flank, an obstacle should be quite impassable—such as a large river, a lake, an impassable swamp. These are all impediments which are rarely met with, and therefore perfect supports for the flanks are seldom to be found, and the want of them is felt now more frequently than formerly, because Armies move more, do not remain so long in one position, consequently require a greater number of positions in the theatre of War.
If the obstacle to approach is not an impassable barrier, then it is, properly speaking, no point d’appui for a flank, it is only a point which strengthens the position. Troops must then be placed behind it, and then again it becomes in relation to these an obstacle to approach.
It is certainly always of advantage to strengthen the flanks in this manner, as fewer troops are then required at those points; but we must take precautions against two things: the first is, placing too much reliance on such supports for the flank, and thus neglecting to have strong reserves behind them; the second is, covering both wings with obstacles of this description, for as they do not completely secure either, they do not prevent the possibility of a combat on both flanks; this may easily become a most disadvantageous defensive, for the obstacles will not allow us easily to sally forth with an active defence on one wing, and thus we may be reduced to defend ourselves in the most unfavourable of all forms, with both flanks thrown back, a d, c b.
(4) These considerations lead again to the deep order
of battle. The less we are able to find secure support for the wings, the more troops we must have in rear, with which we may in turn outflank any portion of the enemy’s army which shall seek to act against our flank.
(5) All kinds of ground which cannot be passed by troops marching in line, all villages, all enclosures of parcels of ground by hedges and ditches, marshy meadows, lastly, all hills which can only be mounted with some difficulty, come under the head of hindrances of this kind, that is, of obstacles that cannot be passed except with difficulty, and slowly; and which, therefore, add greatly to the strength of the troops posted behind them in the combat. Woods can only be included in this category when the underwood is very thick and the ground marshy. A common wood of high trees is as easy to pass as a plain. There is one point, however, in respect to a wood which must not be overlooked, that is, that it may serve to conceal the enemy. If we place ourselves inside it, then there is the same disadvantage for both sides; but it is very dangerous, and at the same time a great mistake to have woods in front or on the flank.* Such a thing can never be allowable unless there are very few roads by which they can be traversed. Abattis intended to bar the passages are so easily removed that they are not of much use.
(6) From all this it follows that we should endeavour to make use of such obstacles upon one flank, in order to offer there a relatively strong resistance with few troops, whilst we carry out our intended offensive on the other flank. With these obstacles, the use of entrenchments may be combined with great advantage, because then, if the enemy passes the obstacle, the fire from the entrenchments may secure our weak force from being overwhelmed by superior numbers, and thrown back too suddenly.
(7) When we are on the defensive, every obstacle covering our front is of great value.
All hills on which positions are taken up are only occupied on this account; for an elevated position has seldom any important influence, often none at all, on the effect of the arms in use. If we stand above the enemy as he approaches, he must ascend with difficulty, therefore he advances only slowly, his ranks get into disorder, and he reaches us with his physical powers exhausted, advantages for us which, with equal bravery and numbers on each side, ought to be decisive. The great effect morally of a rapid charge at full speed is a point which must not on any account be overlooked. The soldier who is advancing becomes insensible even to danger, the one who is standing still loses his presence of mind. It is therefore always advantageous to place the first lines of infantry and artillery on high ground.
If the slope of the hill is so steep, its declivity so broken and uneven, that we cannot sweep it well with our fire, which is often the case, then, instead of placing our front line on the summit ridge, that part should at most only be occupied by skirmishers, and the full line should be so placed on the reverse slope, that at the moment when the enemy reaches the summit ridge and begins to rally his ranks he is exposed to the greatest fire.*
All other local features which form obstacles to approach, such as small rivers, streams, hollow ways, &c., serve to make breaks in the enemy’s front. He must, after passing them, halt to re-form, and that delays him; therefore he should then be brought within range of our most effectual fire. The most effectual fire is case (400 to 600 yards), if there is plenty of artillery available; the fire of musketry (150 to 200 yards), if there is little artillery at hand.
(8) Through this it becomes a rule to include within the zone of our most effective fire every obstacle to approach with which we wish to strengthen our front. But, at the same time, it is important to observe that our whole defence should never depend entirely on our fire, but a considerable portion of our troops (one-third to one-half) should always be kept ready to attack with the bayonet. Therefore, if we are very weak, we must merely place the line of fire (riflemen and artillery) near enough to cover the obstacle with their fire, and place the rest of the troops in columns 600 or 800 yards further back, and if possible under cover.
(9) Another way of making use of obstacles to approach in front is to let them be a little further in front of our line, so that they shall be within the effective range of cannon-shot (1000 to 2000 yards), and if the enemy’s columns pass them, then to attack him from all sides. (At Minden, the Duke Ferdinand did something like this.) In this manner an obstacle of ground is favourable to the plan of actively defending ourselves; and this active defence, of which we have already spoken elsewhere, then takes place on our front.
(10) In the preceding observations, obstacles of ground and country have been considered chiefly as connected lines in relation to extensive positions, but it is necessary to say something about single points.
Isolated points in general can only be defended either by entrenchments or by a strong natural obstacle of ground. Of the first we do not speak at present. Obstacles of ground which, standing isolated, may have to be defended can only be—
(a) Isolated steep Heights.
In this case, entrenchments are indispensable, because the enemy can always advance against the defender with a front more or less extended, and the defender must then at last be taken in rear, because he will rarely be strong enough to show a front on all sides.
Under this term we include every narrow way forming the only approach by which the enemy can reach a particular point. Bridges, embankments, rocky gulleys with precipitous sides, belong to this class.
In respect to all these cases it is to be observed, that either it is impossible for the assailant to turn the obstacle—as, for instance, a bridge over a great river, in which case the defender may then boldly use all his force in order to bring as much fire as possible to bear on the point of passage—or we are not secure against the obstacle being turned—as in the case of bridges over small streams, and the greater number of mountain defiles; then it is necessary to reserve a considerable part of the force (one-third to one-half) for an attack in close order.
(c) Buildings and Enclosures, Villages, small Towns, &c.
If troops are brave, and carry on a War with enthusiasm, there is no place or condition of things in which a few can so well resist many as in the defence of houses. But if we are not quite certain of the men individually, it is better only to occupy the houses, gardens, &c., with riflemen, and to plant guns at the approaches, and to draw up the greater part of the troops (one-third to one-half) in close column, in the place itself, or behind it under cover, in order to rush upon the enemy with this reserve when he attempts to enter.
(11) These isolated posts serve the great operations partly as outposts, not intended to offer an absolute defence, but mostly only to detain the enemy, partly as points which are of importance in the combinations planned for the whole Army. It is also often necessary to hold a distant point, in order to gain time for the development of active defensive measures which we have in view. If the point is remote, it is naturally on that account isolated.
(12) It is only now necessary to add two remarks concerning isolated points, the first is, that we must hold troops in readiness behind these points for the detachments to rally upon in case of being driven out; the second is, that whoever includes such a defence in the series of his combinations should never reckon too much upon it, let the strength of the natural obstacles of ground be ever so great; that, on the other hand, whoever is entrusted with the defence must determine to carry out the object, let circumstances be ever so adverse to him. For this, a spirit of resolution and self-devotion is required which can only spring from a thirst for glory and from enthusiasm: for this reason, men must be chosen for such duties who are not deficient in these noble qualities of the soul.
(13) All that concerns the use of the ground as a means for covering our position and our march up to occupy it requires no elaborate exposition.
We do not now place ourselves on a hill we wish to defend (as was often done formerly) but behind it: we do not place ourselves before a wood, but in it, or behind it; the latter only when we can overlook the wood or thicket. We keep our troops in columns that they may be the more easily concealed; we take advantage of villages, plantations, all undulations of the ground, in order to conceal our troops behind them; in advancing we choose the most broken intersected country,* &c.
In cultivated countries there are hardly any localities so much overlooked that it is not possible by a skilful use of such obstacles and features as the ground presents to keep a great part of the troops on the defensive from being seen. For the assailant, there is more difficulty in keeping a march secret, because he must follow the main loads.
Of course, when the ground is made use of for purposes of concealment of troops, this must be done with a due regard to the end and the combinations which have been decided upon; therefore, in this we must take care above all things that we do not pull to pieces the order of battle, although some small deviations may be allowable.
(14) If we sum up what has now been said on ground, we deduce from it as respects the defensive, that is, the choice of positions, that the following points are those of most importance:
(a) Support of one or both flanks.
(b) Open view before front and flanks.
(c) Obstacles to the approach in front.
(d) Masked positions for troops.
To this is to be added—
(e) A broken country in rear, because that makes pursuit difficult in case of disaster; but no defiles too near (as at Friedland), for that causes delay and confusion.
(15) It would be pedantic to suppose that all these advantages are to be obtained at every position which it is necessary to take up in War. All positions are not of equal importance; their importance increases in proportion to the probability of our being attacked in them. It is only in the most important that we try to combine, if possible, all these advantages; in others we try to do so more or less.
(16) The considerations which the assailant has to study in respect to ground are principally embraced in two leading points: not to choose an over difficult country for the point of attack; and next, on all occasions to advance through the country so that the enemy can see as little as possible of our movements.
(17) I close these observations on the use of ground with a maxim of the highest importance for the defence, and which is to be regarded as the key-stone of the whole theory of defence, which is: Not to expect everything from the strength of the ground, consequently never to be enticed into a passive defence by a strong country. For if the country is in reality so strong that it is impossible for the assailant to drive us out of our position, he will turn it, which is always possible, and then the strongest country is useless; we are then compelled to fight under quite different circumstances, in quite a different country; and we might as well not have included the other locality in our combinations. But if the ground is not of such strength, if it is possible to attack it, still the advantages of such a position will never outweigh the disadvantages of a passive defence. All obstacles of ground must therefore only be taken advantage of for a partial defensive, in order to offer a relatively great resistance with few troops, and to gain time for the offensive, by which the real victory is to be gained at other points.
This is the combination of the singles battles of a War, in order to attain to the object of the campaign.
If we know how to fight, if we know how to conquer, there is not much more wanted; to combine successful results is easy, because it is merely an affair of a well-practised judgment, and does not depend, like the direction of a battle, on special knowledge.
All that is essential in the few principles which there are, and which depend chiefly on the constitution of States and Armies may, therefore, be brought within a small compass.
[* ]Modern practice has altered this. Nothing serves better to hamper unity of command in attacking troops than small woods, whose exits are under close fire from the defender’s position.—Editor.
[* ]This was the British practice in the Peninsula and at Waterloo, At Ligny the Prussians stood on the enemy’s side of the hill. Wellington, seeing this from Bry, said, “Old Blücher will get most damnably mauled.”—Editor.
[* ]This no longer holds good. At St. Privat the Prussians attacking across the open carried the position, at Gravelotte the ground being intersected they failed completely. Unity of command is more essential than cover from fire.—Editor.