ven of
a single one leads to death" (Marshal Foch). At almost any period of
the battle, and in almost every phase of fighting, surprise can be
brought about by a sudden and unexpected outburst of effective machine
gun or other form of fire. "A sudden effective fire will have a
particularly demoralising effect on the enemy; it is often
advantageous, therefore, to seek for surprise effects of this sort by
temporarily withholding fire" ("Infantry Training, 1921").

THE DECISIVE BLOW.--The preparatory action and the development usually
take the form of a converging movement of separated forces, so timed as
to strike the adversary's front and flank simultaneously, in order to
threaten the enemy's line of communications, for the line of supply is
as vital to the existence of an army as the heart to the life of a
human being. "Perhaps no situation is more pitiable than that of a
commander who has permitted an enemy to sever his communications. He
sees the end of his resources at hand, but not the means to replenish
them" (General Sir E. B. Hamley). The decisive blow will be delivered
by the General Reserve, which will be secretly concentrated and
launched as secretly as possible; and the commander of the whole force
will so distribute his troops that about half his available force can
be kept in hand for this decisive blow, on a part of the enemy's front
if sufficient penetration has been effected, or on a flank. The point
chosen becomes the vital {32} point, and success there means success at
all points. Once routed, the enemy must be relentlessly pursued and
prevented from regaining order and moral.

A battle was fought in the year B.C. 331, nearly 2,300 years ago, at
Arbela,[1] in Mesopotamia, the Eastern theatre of operations in the
Great War of 1914-18, and it deserves study to show the eternal nature
of the main principles which underlie the Art of War. Alexander the
Great invaded the territories of Darius, King of the Medes and
Persians, with the strategic aim of defeating his adversary's main
armies in a decisive battle. The Macedonian forces were preceded by an
Advanced Guard of Cavalry, and from information obtained by the
Vanguard, Alexander was made aware of the strength and position of the
Persian forces. By a careful reconnaissance of the ground in company
with his Corps Commanders, Alexander was able to forestall a projected
movement, and by advancing in two lines of battle in such a way that
his tro