White arranges his twelve units into four quarters of three each, and places one quarter at each corner of a square thus:—­

[Illustration:  Sketch 22.]

We will give them titles, and call them A, B, C, and D.

If, as is most generally the case in a defensive campaign at its opening, White cannot be certain from which exact direction the main blow is coming, he may yet know that it is coming from some one general direction, from one sector of the compass at least, and he arranges his square to face towards that sector.

For instance, in the above diagram, he may not know whether the blow is coming from the precise direction 1, or 2, or 3, but he knows that it is coming somewhere within the sector XY.

Then he will draw up his square so that its various bodies all face towards the average direction from which the blow may come.

The SIZE of his square—­which is of great importance to the result—­he makes as restricted as possible, subject to two prime conditions.  These conditions are:—­

First, that there shall be room for the troops composing each corner to be deployed—­that is, spread out for fighting.  Secondly, that there shall be room between any two corners (A and C, for instance) for a third corner (D, for instance) to move in between them and spread out for fighting in support of them.  He makes his square as close and restricted as possible, because his success depends—­as will be seen in a moment—­upon the rapidity with which any one corner can come up in support of the others.  But he leaves enough room for the full numbers to spread out for fighting, because otherwise he loses in efficiency; and he leaves room enough between any two squares for a third one to come in, because the whole point of the formation is the aid each corner can bring to the others.

In this posture he awaits the enemy.

That enemy will necessarily come on in a lengthy line, lengthy in proportion to the number of his units.  For it is essential to the general commanding superior numbers to make the whole of the superior numbers tell, and this can only be done if they march along parallel roads, and these roads are sufficiently wide apart for the various columns to have plenty of room to deploy—­that is, to spread out into a fighting line—­when the shock comes.

[Illustration:  Sketch 23.]

This extended line of Black marching thus against White strikes White first upon some one corner of his square.  Suppose that corner to be corner A. Then the position when contact is established and the first serious fighting begins is what you will observe in the above diagram.  A is the corner (now spread out for fighting) which gets the first shock.

Note you (for this is the crucial point of the whole business) that upon the exposed corner A will fall a very dangerous task indeed.  A will certainly be attacked by forces superior to itself.  Normally forces more than half as large again as A will be near enough to A to concentrate upon him in the first shock.  The odds will be at least as much as five to three, the Black units, 4, 5, and 6, will be right on A, and 3 and 7 will be near enough to come in as well in the first day or two of the combat, while possibly 2 may have a look in as well.