How was it that—­whilst we landed invading armies in many hostile countries, seized many portions of hostile territory, and drove more than one enemy’s commerce from the sea—­our own country has been free from successful invasion for more than eight centuries, few portions of our territory have been taken from us even temporarily, and our commerce has increased throughout protracted maritime wars?  To this there can only be one answer, viz. that the arrangements for defence were effectual.  What, then, were these arrangements?  They were comprised in the provision of a powerful, well-distributed, well-handled navy, and of a mobile army of suitable strength.  It is to be observed that each element possessed the characteristic of mobility.  We have to deal here more especially with the naval element, and we must study the manner in which it operates.

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.