It must always be remembered that, except as a preparation or a cover for offensive action, the defensive is seldom or never of any use; for by the continued use of the defensive alone nothing can be acquired, though the enemy may be prevented from acquiring anything.  But where we are too weak to assume the offensive it is often necessary to assume the defensive, and wait in expectation of time turning the scale in our favour and permitting us to accumulate strength relatively greater than the enemy’s; we then pass to the offensive, for which our defensive has been a preparation.  At sea we have had little occasion for the defensive as a general plan.  But that is no reason for neglecting its study.  In despising the defensive ourselves we have consistently ignored the strength it gives our enemies.  The bulk of our naval history is the story of how we have been baffled and thwarted by our enemies assuming the defensive at sea in support of their offensive on land.  We have seldom succeeded in treating this attitude with success, and it is only by studying the defensive we can hope to do so.

Offensive Operations used with a Defensive Intention

(A) Counter attacks. 
(B) Diversions.

Counter attacks are those which are made upon an enemy who exposes himself anywhere in the theatre of his offensive operations.  It is this form of attack which constitutes what Clausewitz calls the “surprise advantage of defence.”

Diversions are similar operations undertaken against an enemy outside the limit of his theatre of offensive operations.

Diversions are designed to confuse his strategy, to distract his attention, and to draw off his forces from his main attack.  If well planned, they should divert a force greater than their own.  They should, therefore, be small.  The nearer they approach the importance of a real attack the less likely they are to divert a force greater than their own.

Diversions involve a breach of the law of concentration, and it is only their power of diverting or containing a larger force than their own that justifies their use.

This power depends mainly on suddenness and mobility, and these qualities are most highly developed in combined expeditions.

Diversions must be carefully distinguished from eccentric attacks.  Eccentric attacks are true offensive movements.  They have a positive object, i.e., they aim to acquire something from the enemy; whereas diversions have a negative object, i.e., they aim at preventing the enemy doing or acquiring something.  Eccentric attacks are usually made in greater force than diversions.