The primary method, then, in which we use victory or preponderance at sea and bring it to bear on the enemy's population to secure peace, is by the capture or destruction of the enemy's property, whether public or private. But in comparing the process with the analogous occupation of territory and the levying of contributions and requisitions we have to
observe a marked difference. Both processes are what may be called economic pressure. But ashore the economic pressure can only be exerted as the consequence of victory or acquired domination by military success. At sea the process begins at once. Indeed, more often than not, the first act of hostility in maritime wars has been the capture of private property at sea. In a sense this is also true ashore. The first step of an invader after crossing the frontier will be to control to a less or greater extent such private property as he is able to use for his purposes. But such interference with private property is essentially a military act, and does not belong to the secondary phase of economic pressure. At sea it does, and the reason why this should be so lies in certain fundamental differences between land and sea warfare which are implicit in the communication theory of naval war.
To elucidate the point, it must be repeated that maritime communications, which are the root of the idea of command of the sea, are not analogous to military communications in the ordinary use of the term. Military communications refer solely to the army's lines of supply and retreat. Maritime communications have a wider meaning. Though in effect embracing the lines of fleet supply, they correspond in strategical values not to military lines of supply, but to those internal lines of communication by which the flow of national life is maintained ashore. Consequently maritime communications are on a wholly different footing from land communications. At sea the communications are, for the most part, common to both belligerents, whereas ashore each possesses his own in his own territory. The strategical effect is of far-reaching importance, for it means that at sea strategical offence and defence tend to merge in a way that is unknown ashore. Since maritime communications are common, we as a rule cannot attack those of the enemy without defending our own. In military operations the converse is the rule. Normally, an attack on our enemy's communications tends to expose their own.
The theory of common communications will become clear by taking an example. In our wars with France our communications with the Mediterranean, India, and America ran down from the Channel mouth past Finisterre and St. Vincent; and those of France, at least from her Atlantic ports, were identical for almost their entire distance. In our wars with the Dutch the identity was even closer. Even in the case of Spain, her great trade routes followed the same lines as our own for the greater part of their extent. Consequently the opening moves which we generally made to defend our trade by the occupation of those lines placed us in a position to attack our enemy's trade. The same situation arose even when our opening dispositions were designed as defence against home invasion or against attacks upon our colonies, for the positions our fleet had to take up to those ends always lay on or about the terminal and focal points of trade routes. Whether our immediate object were to bring the enemy's main fleets to action or to exercise economic pressure, it made but little difference. If the enemy were equally anxious to engage, it was at one of the terminal or focal areas we were almost certain to get contact. If he wished to avoid a decision, the best way to force him to action was to occupy his trade routes at the same vital points.
Thus it comes about that, whereas on land the process of economic pressure, at least in the modern conception of war, should only begin after decisive victory, at sea it starts automatically from the first. Indeed such pressure may be the only means of forcing the decision we seek, as will appear more clearly when we come to deal with the other fundamental difference between land and sea warfare.
Meanwhile we may note that at sea the use of economic
pressure from the commencement is justified for two reasons. The first is, as we have seen, that it is an economy of means to use our defensive positions for attack when attack does not vitiate those positions, and it will not vitiate them if fleet cruisers operate with restraint. The second is, that interference with the enemy's trade has two aspects. It is not only a means of exerting the secondary economic pressure, it is also a primary means towards overthrowing the enemy's power of resistance. Wars are not decided exclusively by military and naval force. Finance is scarcely less important. When other things are equal, it is the longer purse that wins. It has even many times redressed an unfavourable balance of armed force and given victory to the physically weaker Power. Anything, therefore, which we are able to achieve towards crippling our enemy's finance is a direct step to his overthrow, and the most effective means we can employ to this end against a maritime State is to deny him the resources of seaborne trade.
It will be seen, therefore, that in naval warfare, however closely we may concentrate our efforts on the destruction of our enemy's armed forces as the direct means to his overthrow, it would be folly to stay our hands when opportunities occur, as they will automatically, for undermining his financial position on which the continued vigour of those armed forces so largely depends. Thus the occupation of our enemy's sea communications and the confiscatory operations it connotes are in a sense primary operations, and not, as on land, secondary.
Such, then, are the abstract conclusions at which we arrive in our attempt to analyse the idea of command of the sea and to give it precision as the control of common communications. Their concrete value will appear when we come to deal with the various forms which naval operations may take, such as, "seeking out the enemy's fleet," blockade, attack and defence of trade, and the safeguarding of combined expeditions.