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.

A, thus tackled, has become what may be called "the _operative corner_
of the square." It is his task "to retreat and hold the enemy" while
B, C, and D, "the masses of manoeuvre," swing up. But under that
simple phrase "operative corner" is hidden all the awful business of a
fighting retreat: it means leaving your wounded behind you, marching
night and day, with your men under the impression of defeat; leaving
your disabled guns behind you, keeping up liaison between all your