A fleet suffers one fundamental limitation on its freedom of action――it is tied to the sea. Hence it cannot strike directly at the hostile nation. Its action is either directed against the enemy’s stomach, and through that to his moral, or in conveying and serving as a floating base for troops or aircraft. As with land warfare, the destruction of the enemy’s main fleet is often spoken of as the objective, whereas in reality this act is but a means towards it――by the destruction of the enemy’s shield the way is opened for a more effective blockade or for the landing of an army. Like land warfare, also, the knowledge that its coasts are thus rendered defenceless, may cause a nation to sue for peace rather than await inevitable starvation or invasion. But just as the value of armies has been radically affected by the conquest of the air, so has that of surface fleets by the coming of that other new and three-dimensional weapon, the submarine. Instead of hopping over the enemy’s shield as does the aeroplane, the submarine dives under it. In the Great War a submarine blockade almost brought the supreme naval power to its knees by starvation――yet Germany never had more than 175 submarines. The fundamental purpose of a navy is to protect a nation’s sea communications and sever those of the enemy, and as, therefore, _blockade_ is the main offensive _rôle_ of the naval weapon, it behooves us to examine the future of this means to the moral objective. Since the war controversy has raged round the respective merits of the battleship, submarine, and naval aeroplane, as _destructive weapons_. Into this I have no intention of entering――not only because the problem demands a technical knowledge of sea warfare to which I have no pretensions, but also because the rival arguments, in their absorption with a means, overlook the end. Steering clear of the Sargasso Sea of technical values, let us rather direct our course, by the compass of grand strategy, on the true objective of the naval weapon. Nations cannot afford to stake their existence on a gamble in “futures,” and therefore until a new weapon has attained an all-round superiority to the existing ones, it would be rash to adopt it exclusively. The battleship retains the sovereignty of the _oceans_ for some time to come at least, but in the _narrow seas_ has yielded pride of place to the submarine――if the lessons of the Great War be assessed. Here is the crux of the matter. Thus France is wise in concentrating mainly on the new weapon, whereas Great Britain and the United States, being concerned equally with ocean communications, cannot yet afford to abandon the surface-going capital ship. The vital question of the future is how this transfer of power over the narrow seas affects the international situation――particularly that of Great Britain, which is concerned with both spheres of sea-power.