successes, the advance of November 20, 1917, will ever remain an example of the value of surprise in war. "Surprise strikes with terror even those who are by far the stronger. A new weapon of war may ensure it, or a sudden appearance of a force larger than the adversary's, or a concentration of forces upon a point at which the adversary is not ready instantaneously to parry the blow. But if the methods {31} be various, the aim is always to produce the same moral effect upon the enemy--terror--by creating in him at the swift apparition of unexpected and incontestably powerful means, the sentiment of impotence, the conviction that he cannot conquer--that is to say, that he is conquered. And this supreme blow of unexpected vigour need not be directed upon the whole of the enemy's army. For an army is an animate and organised being, a collection of organs, of which the loss even 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.