The only safe method is to inquire what it is we can secure for ourselves, and what it is we can deny the enemy by command of the sea.  Now, if we exclude fishery rights, which are irrelevant to the present matter, the only right we or our enemy can have on the sea is the right of passage; in other words, the only positive value which the high seas have for national life is as a means of communication.  For the active life of a nation such means may stand for much or it may stand for little, but to every maritime State it has some value.  Consequently by denying an enemy this means of passage we check the movement of his national life at sea in the same kind of way that we check it on land by occupying his territory.  So far the analogy holds good, but no further.

So much for the positive value which the sea has in national life.  It has also a negative value.  For not only is it a means of communication, but, unlike the means of communication ashore, it is also a barrier.  By winning command of the sea we remove that barrier from our own path, thereby placing ourselves in position to exert direct military pressure upon the national life of our enemy ashore, while at the same time we solidify it against him and prevent his exerting direct military pressure upon ourselves.

Command of the sea, therefore, means nothing but the control of maritime communications, whether for commercial or military purposes.  The object of naval warfare is the control of communications, and not, as in land warfare, the conquest of territory.  The difference is fundamental.  True, it is rightly said that strategy ashore is mainly a question of communications, but they are communications in another sense.  The phrase refers to the communications of the army alone, and not to the wider communications which are part of the life of the nation.

But on land also there are communications of a kind which are essential to national life—­the internal communications which connect the points of distribution.  Here again we touch an analogy between the two kinds of war.  Land warfare, as the most devoted adherents of the modern view admit, cannot attain its end by military victories alone.  The destruction of your enemy’s forces will not avail for certain unless you have in reserve sufficient force to complete the occupation of his inland communications and principal points of distribution.  This power is the real fruit of victory, the power to strangle the whole national life.  It is not until this is done that a high-spirited nation, whose whole heart is in the war, will consent to make peace and do your will.  It is precisely in the same way that the command of the sea works towards peace, though of course in a far less coercive manner, against a continental State.  By occupying her maritime communications and closing the points of distribution in which they terminate we destroy the national life afloat, and thereby check the vitality of that life ashore so far as the one is dependent on the other.  Thus we see that so long as we retain the power and right to stop maritime communications, the analogy between command of the sea and the conquest of territory is in this aspect very close.  And the analogy is of the utmost practical importance, for on it turns the most burning question of maritime war, which it will be well to deal with in this place.