A necessary consequence of an enemy's exclusion from the combined line as it approaches the territory to be defended is--as already suggested--that invasion of that territory and serious raids upon it will be rendered impracticable. Indeed, if the exclusion be absolutely complete and permanent, raids of every kind and depredations on commerce in the neighbourhood will be prevented altogether. It should be explained that though lines and communications are spoken of, it is the area crossed by them which is strategically important. A naval force, either guarding or intending to assail a line, does not necessarily station itself permanently upon it. All that it has to do is to remain, for the proper length of time, within the strategic area across which the defended or threatened line runs. The strategic area will be of varying extent, its boundaries being determined by circumstances. The object of the defence will be to make the area from which the enemy's ships are excluded as extensive as possible. When the enemy has been pushed back into his own waters and into his own ports the exclusion is strategically complete. The sea is denied to his invading and important raiding expeditions, and indeed to most of his individual cruisers. At the same time it is free to the other belligerent. To effect this a vigorous offensive will be necessary. The immediate theatre of operations, the critical strategic area, need not be, and often ought not to be, near the territory defended by our navy. It is necessary to dwell upon this, because no principle of naval warfare has been more frequently or more seriously misapprehended. Misapprehension of it has led to mischievous and dangerous distribution of naval force and to the squandering of immense sums of money on local defence vessels; that is, vessels only capable of operating in the very waters from which every effort should be made to exclude the enemy. Failure to exclude him from them can only be regarded as, at the very least, yielding to him an important point in the great game of war. If we succeed in keeping him away, the local defence craft of every class are useless, and the money spent on them has been worse than wasted, because, if it had not been so spent, it might have been devoted to strengthening the kind of force which must be used to keep the enemy where he ought to be kept, viz. at a distance from our own waters.