Before Mahan proved his doctrine, it was felt in a general way that sea power was necessary to the prosperity and security of a nation.  Mahan was not the first to have this idea, for it had been in the minds of some men, and in the policy of one nation, for more than a century.  Neither was Mahan the first to put forth the idea in writing; but he was the first to make an absolute demonstration of the truth.  Newton was not the first man to know, or to say, that things near the earth tend to fall to the earth; but he was the first to formulate and prove the doctrine of universal gravitation.  In the same way, all through history, we find that a few master minds have been able to group what had theretofore seemed unrelated phenomena, and deduce from them certain laws.  In this way they substituted reasoning for speculation, fact for fancy, wisdom for opportunism, and became the guides of the human race.

The effect of the acceptance of Mahan’s doctrine was felt at once.  Realizing that the influence of sea power was a fact, comprehending Great Britain’s secret, after Mahan had disclosed it, certain other great nations of the world, especially Germany, immediately started with confidence and vigor upon the increase of their own sea power, and pushed it to a degree before unparalleled; with a result that must have been amazing to the man who, more than any other, was responsible for it.

Since the words “sea power,” or their translation, is a recognized phrase the world over, and since the power of sea power is greater than ever before, and is still increasing, it may be profitable to consider sea power as an entity, and to inquire what are its leading characteristics, and in what it mainly consists.

There is no trouble in defining what the sea is, but there is a good deal of trouble in defining what power is.  If we look in a dictionary, we shall find a good many definitions of power; so many as to show that there are many different kinds of power, and that when we read of “power,” it is necessary to know what kind of power is meant.  Clearly “sea power” means power on the sea.  But what kind of power?  There are two large classes into which power may be divided, passive and active.  Certainly we seem justified, at the start, in declaring that the power meant by Mahan was not passive, but active.  Should this be granted, we cannot be far from right if we go a step further, and declare that sea power means ability to do something on the sea.

If we ask what the something is that sea power has ability to do, we at once perceive that sea power may be divided into two parts, commercial power and naval power.

The power exerted by commercial sea power is clearly that exerted by the merchant service, and is mainly the power of acquiring money.  It is true that the merchant service has the power of rendering certain services in war, especially the power of providing auxiliary vessels, and of furnishing men accustomed to the sea; but as time goes on the power contributable by the merchant service must steadily decrease, because of the relatively increasing power of the naval service, and the rapidly increasing difference between the characteristics of ships and men suitable for the merchant service and those suitable for the naval service.