If we consider the combat no longer in itself but in relation to the other forces of War, then its duration acquires a special importance.
This duration is to be regarded to a certain extent as a second subordinate success. For the conqueror the combat can never be finished too quickly, for the vanquished it can never last too long. A speedy victory indicates a higher power of victory, a tardy decision is, on the side of the defeated, some compensation for the loss.
This is in general true, but it acquires a practical importance in its application to those combats, the object of which is a relative defence.
Here the whole success often lies in the mere duration. This is the reason why we have included it amongst the strategic elements.
The duration of a combat is necessarily bound up with its essential relations. These relations are, absolute magnitude of force, relation of force and of the different arms mutually, and nature of the country. Twenty thousand men do not wear themselves out upon one another as quickly as two thousand: we cannot resist an enemy double or three times our strength as long as one of the same strength; a cavalry combat is decided sooner than an infantry combat; and a combat between infantry only, quicker than if there is artillery [The increase in the relative range of artillery and the introduction of shrapnel has altogether modified this conclusion] as well; in hills and forests we cannot advance as quickly as on a level country; all this is clear enough.
From this it follows, therefore, that strength, relation of the three arms, and position, must be considered if the combat is to fulfil an object by its duration; but to set up this rule was of less importance to us in our present considerations than to connect with it at once the chief results which experience gives us on the subject.
Even the resistance of an ordinary Division of 8000 to 10,000 men of all arms even opposed to an enemy considerably superior in numbers, will last several hours, if the advantages of country are not too preponderating, and if the enemy is only a little, or not at all, superior in numbers, the combat will last half a day. A Corps of three or four Divisions will prolong it to double the time; an Army of 80,000 or 100,000 to three or four times. Therefore the masses may be left to themselves for that length of time, and no separate combat takes place if within that time other forces can be brought up, whose co-operation mingles then at once into one stream with the results of the combat which has taken place.
These calculations are the result of experience; but it is important to us at the same time to characterise more particularly the moment of the decision, and consequently the termination.