Let us suppose that White swings to the left.
Mark what follows. The distances which White's units have got to go are comparatively small. B will be up at A's side, and so will D in a short time after the swing is over, and when the swing is completed, the position is after this fashion. Black's numbers, 1 to 9 inclusive, find themselves tackled by all Black's twelve. There is a superiority of number against Black on his right, White's left, and the remaining part of Black's line (10 to 16 inclusive), is out in the cold.
If it were a tactical problem, and all this were taking place in a small field, Black's left wing, 10-16, would, of course, come up at once and redress the balance. But being a strategical problem, and involving very large numbers and very great distances, Black's left wing, 10-16, can do nothing of the kind. For Black's left wing, 10-16, cannot possibly get up in time. Long before it has arrived on the scene, White's 12 will have broken Black's 9 along Black's right wing.
Sketch 27.
There are three elements which impose this delay upon Black's left wing.
First, to come round in aid of the right wing means the marching forward of one unit after another, so that each shall overlap the last, and so allow the whole lot to come up freely. This means that the last unit will have to go forward six places before turning, and that means several days' marching. For with very large bodies, and with a matter of 100 miles to come up, all in one column, it would be an endless business (Sketch 28).
Sketch 28.
Next you have the delay caused by the conversion of direction through a whole right angle. That cause of delay is serious. For when you are dealing with very large bodies of men, such as half a dozen army corps, to change suddenly from the direction S (see Sketch 29) for which your Staff work was planned, and to break off at a moment's notice in direction E, while you are on the march towards S, is impossible. You have to think out a whole new set of dispositions, and to re-order all your great body of men. White was under no such compulsion, for though he had to swing, the swing faced the same general direction as his original dispositions. And the size of the units and the distances to be traversed—the fact that the problem is strategical and not tactical—is the essence of the whole thing. If, for instance, you have (as in Sketch 30) half a dozen, not army corps, but mere battalions of 1,000 men, deployed over half a dozen miles of ground, AB, and advancing in the direction SS, and they are suddenly sent for in the direction E, it is simple enough. You form your 6,000 men into column; in a few hours' delay they go off in the direction E, and when they get to the place where they are wanted, the column can spread out quickly again on the front CD, and soon begin to take part in the action. But when you are dealing with half a dozen army corps—240,000 men—it is quite another matter. The turning of any one of these great bodies through a whole right angle is a lengthy business. You cannot put a quarter of a million men into one column—they would take ages to deploy—so you must, as we have seen, make each unit of them overlap the next before the turn can begin.