Naval war is sea-power in action; and sea-power, taken in the narrow sense, has limitations. It may not, even when so taken, cease to act at the enemy's coast-line, but its direct influence extends only to the inner side of a narrow zone conforming to that line. In a maritime contest each side tries to control the ocean communications and to prevent the other from controlling them. If either gains the control, something in addition to sea-power strictly defined may begin to operate: the other side's territory may be invaded or harassed by considerable raids, and its commerce may be driven from the sea. It will be noticed that control of ocean communications is the needful preliminary to these. It is merely a variant of the often employed expression of the necessity, in war, of obtaining command of the sea. In the case of the most important portion of the British Empire, viz. the United Kingdom, our loss of control of the ocean communications would have a result which scarcely any foreign country would experience. Other countries are dependent on importations for some part of the food of their population and of the raw material of their industry; but much of the importation is, and perhaps all of it may be, effected by land. Here, we depend upon imports from abroad for a very large part of the food of our people, and of the raw material essential to the manufacture of the commodities by the exchange of which we obtain necessary supplies; and the whole of these imports come, and must come to us, by sea. Also, if we had not freedom of exportation, our wealth and the means of supporting a war would disappear. Probably all the greater colonies and India could feed their inhabitants for a moderately long time without sea-borne imports, but unless the sea were open to them their prosperity would decline. This teaches us the necessity to the British Empire of controlling our maritime communications, and equally teaches those who may one day be our enemies the advisability of preventing us from doing so. The lesson in either case is driven farther home by other considerations connected with communications. In war a belligerent has two tasks before him. He has to defend himself and hurt his enemy. The more he hurts his enemy, the less is he likely to be hurt himself. This defines the great principle of offensive defence. To act in accordance with this principle, a belligerent should try, as the saying goes, to carry the war into the enemy's country. He should try to make his opponents fight where he wants them to fight, which will probably be as far as possible from his own territory and as near as possible to theirs. Unless he can do this, invasion and even serious raids by him will be out of the question. More than that, his inability to do it will virtually indicate that on its part the other side can fix the scene of active hostilities unpleasantly close to the points from which he desires to keep its forces away.