_That is exactly what happened in the first three weeks of active
operations in the West. The operative corner A in the annexed diagram
was the Franco-British force upon the Sambre. The retirement of that
operative corner and its holding of the enemy was what is called in
this country "The Retreat from Mons." BB are the "masses of manoeuvre"
behind A. The swinging up of these masses involving the retirement of
the whole was the Battle of the Marne._

[Illustration: Sketch 31.]

Now, it is evident that in all this everything depends upon the
tenacity and military value of the operative corner, which is exposed
and sacrificed that the whole scheme of the Open Square may work.

If that operative corner is destroyed as a force--is overwhelmed or
dispersed or surrounded--while it is fighting its great odds, the
whole square goes to pieces. Its centre is penetrated by the enemy,
and the army is in a far worse plight than if recourse had never been
had to the open strategic square at all. For if the operative corner,
A, is out of existence before the various bodies forming the
"manoeuvring mass" behind it have had time to "swing," then the enemy
will be right in their midst, and destroying, in overwhelming force,
these remaining _separated_ bodies in detail.

It was here that the German strategic theory contrasted so violently
with the French. The Germans maintained that an ordeal which Napoleon
might have been able to live through with his veterans and after
fifteen years of successful war, a modern conscript army, most of its
men just taken from civilian life and all of short service, would
never endure. They believed the operative corner would go to pieces