The events of the long period which we have been considering will have shown how sea-power operates, and what it effects.  What is in it will have appeared from this narrative more clearly than would have been possible from any mere definition.  Like many other things, sea-power is composed of several elements.  To reach the highest degree of efficacy it should be based upon a population naturally maritime, and on an ocean commerce naturally developed rather than artificially enticed to extend itself.  Its outward and visible sign is a navy, strong in the discipline, skill, and courage of a numerous personnel habituated to the sea, in the number and quality of its ships, in the excellence of its materiel, and in the efficiency, scale, security, and geographical position of its arsenals and bases.  History has demonstrated that sea-power thus conditioned can gain any purely maritime object, can protect the trade and the communications of a widely extended empire, and whilst so doing can ward off from its shores a formidable invader.  There are, however, limitations to be noted.  Left to itself its operation is confined to the water, or at any rate to the inner edge of a narrow zone of coast.  It prepares the way for the advance of an army, the work of which it is not intended, and is unable to perform.  Behind it, in the territory of which it guards the shores, there must be a land-force adjusted in organisation, equipment, and numbers to the circumstances of the country.  The possession of a navy does not permit a sea-surrounded state to dispense with all fixed defences or fortification; but it does render it unnecessary and indeed absurd that they should be abundant or gigantic.  The danger which always impends over the sea-power of any country is that, after being long unused, it may lose touch of the sea.  The revolution in the constructive arts during the last half-century, which has also been a period of but little-interrupted naval peace, and the universal adoption of mechanical appliances, both for ship-propulsion and for many minor services—­mere materiel being thereby raised in the general estimation far above really more important matters—­makes the danger mentioned more menacing in the present age than it has ever been before.

II

THE COMMAND OF THE SEA[50]

[Footnote 50:  Written in 1899. (EncyclopoediaBritannica_.)]

This phrase, a technical term of naval warfare, indicates a definite strategical condition.  The term has been substituted occasionally, but less frequently of late years, for the much older ’Dominion of the sea’ or ‘Sovereignty of the sea,’ a legal term expressing a claim, if not a right.  It has also been sometimes treated as though it were identical with the rhetorical expression ’Empire of the sea.’  Mahan, instead of it, uses the term ’Control of the sea,’ which has the merit of precision, and is not likely to be misunderstood