Front Page Titles (by Subject) CHAPTER IV: CONVERGENCE OF ATTACK AND DIVERGENCE OF DEFENCE - On War, vol. 2
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CHAPTER IV: CONVERGENCE OF ATTACK AND DIVERGENCE OF DEFENCE - 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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CONVERGENCE OF ATTACK AND DIVERGENCE OF DEFENCE
These two conceptions, these forms in the use of offensive and defensive, appear so frequently in theory and reality, that the imagination is involuntarily disposed to look upon them as intrinsic forms, necessary to attack and defence, which, however, is not really the case, as the smallest reflection will show. We take the earliest opportunity of examining them, that we may obtain once for all clear ideas respecting them, and that, in proceeding with our consideration of the relations of attack and defence, we may be able to set these conceptions aside altogether, and not have our attention for ever distracted by the appearance of advantage and the reverse which they cast upon things. We treat them here as pure abstractions, extract the conception of them like an essence, and reserve our remarks on the part which it has in actual things for a future time.
The defending party, both in tactics and in Strategy, is supposed to be waiting in expectation, therefore standing, whilst the assailant is imagined to be in movement, and in movement expressly directed against that standing adversary. It follows from this, necessarily, that turning and enveloping is at the option of the assailant only, that is to say, as long as his movement and the immobility of the defensive continue. This freedom of choice of the mode of attack, whether it shall be convergent or not, according as it shall appear advantageous or otherwise, ought to be reckoned as an advantage to the offensive in general. But this choice is free only in tactics; it is not always allowed in Strategy. In the first, the points on which the wings rest are hardly ever absolutely secure; but they are very frequently so in Strategy, as when the front to be defended stretches in a straight line from one sea to another, or from one neutral territory to another. In such cases, the attack cannot be made in a convergent form, and the liberty of choice is limited. It is limited in a still more embarrassing manner if the assailant is obliged to operate by converging lines. Russia and France cannot attack Germany in any other way than by converging lines; therefore they cannot attack with their forces united. Now if we assume as granted that the concentric form in the action of forces in the majority of cases is the weaker form, then the advantage which the assailant possesses in the greater freedom of choice may probably be completely outweighed by the disadvantage, in other cases, of being compelled to make use of the weaker form.
We proceed to examine more closely the action of these forms, both in tactics and in Strategy.
It has been considered one of the chief advantages of giving a concentric direction to forces, that is, operating from the circumference of a circle towards the centre, that the further the forces advance, the nearer they approach to each other; the fact is true, but the supposed advantage is not; for the tendency to union is going on equally on both sides; consequently, the equilibrium is not disturbed. It is the same in the dispersion of force by eccentric movements.
But another and a real advantage is, that forces operating on converging lines direct their action towards a common point, those operating on diverging lines do not.—Now what are the effects of the action in the two cases? Here we must separate tactics from strategy.
We shall not push the analysis too far, and therefore confine ourselves to the following points as the advantages of the action in tactics.
1. A cross fire, or, at least, an increased effect of fire, as soon as all is brought within a certain range.
2. Attack of one and the same point from several sides.
3. The cutting off the retreat.
The interception of a retreat may be also conceived strategically, but then it is plainly much more difficult, because great spaces are not easily blocked. The attack upon one and the same body from several quarters is generally more effectual and decisive, the smaller this body is, the nearer it approaches to the lowest limit—that of a single combatant. An Army can easily give battle on several sides, a Division less easily, a battalion only when formed in mass, a single man not at all. Now Strategy, in its province, deals with large masses of men, extensive spaces and considerable duration of time; with tactics, it is the reverse. From this follows that the attack from several sides in Strategy cannot have the same results as in tactics.
The effect of fire does not come within the scope of Strategy; but in its place there is something else. It is that tottering of the base which every Army feels when there is a victorious enemy in its rear, whether near or far off.
It is, therefore, certain that the concentric action of forces has an advantage in this way, that the action or effect against a is at the same time one against b, without its force against a being diminished, and that the action against b is likewise action against a. The whole, therefore, is not a+b, but something more; and this advantage is produced both in tactics and Strategy, although somewhat differently in each.
Now what is there in the eccentric or divergent action of forces to oppose to this advantage? Plainly the advantage of having the forces in greater proximity to each other, and the moving on interior lines. It is unnecessary to demonstrate how this can become such a multiplier of forces that the assailant cannot encounter the advantage it gives his opponent unless he has a great superiority of force.—When once the defensive has adopted the principle of movement (movement which certainly commences later than that of the assailant, but still time enough to break the chains of paralysing inaction), then this advantage of greater concentration and the interior lines tends much more decisively, and in most cases more effectually, towards victory than the concentric form of the attack. But victory must precede the realisation of this superiority; we must conquer before we can think of cutting off an enemy’s retreat. In short, we see that there is here a relation similar to that which exists between attack and defence generally; the concentric form leads to brilliant results, the advantages of the eccentric are more secure: the former is the weaker form with the positive object; the latter, the stronger form with the negative object. In this way these two forms seem to us to be brought nearly to an even balance. Now if we add to this that the defence, not being always absolute, is also not always precluded from using its forces on converging lines, we have no longer a right to believe that this converging form is alone sufficient to ensure to the offensive a superiority over the defensive universally, and thus we set ourselves free from the influence which that opinion usually exercises over the judgment, whenever there is an opportunity.
What has been said up to the present, relates to both tactics and Strategy; we have still a most important point to bring forward, which applies to Strategy only. The advantage of interior lines increases with the distances to which these lines relate. In distances of a few thousand yards, or a couple of miles, the time which is gained, cannot of course be as much as in distances of several days’ march, or indeed, of one hundred or one hundred and fifty miles; the first, that is, the small distances, concerns tactics, the greater ones belong to Strategy. But, although we certainly require more time to reach an object in Strategy, than in tactics, and an Army is not so quickly defeated as a battalion, still, these periods of time in Strategy can only increase up to a certain point; that is, they can only last until a battle takes place, or, perhaps, over and above that, for a few days during which a battle may be avoided without serious loss. Further, there is a much greater difference in the real start in advance, which is gained in one case, as compared with the other. Owing to the insignificance of the distances in tactics, the movements of one Army in a battle take place almost in sight of the other; the Army, therefore, on the exterior line, will generally very soon be made aware of what his adversary is doing. From the long distances, with which Strategy has to deal, it very seldom happens that the movement of one Army is not concealed from the other for at least a day, and there are numerous instances, in which especially if the movement is only partial, such as a considerable detachment, that it remains secret for weeks.—It is easy to see, what a great advantage this power of concealing movements must be to that party, who through the nature of his position has reason to desire it most.
We here close our considerations on the convergent and divergent use of forces, and the relation of those forms to attack and defence, proposing to return to the subject at another time.