Under the term blockade we include operations which vary widely in character and in strategical intention. In the first place, blockade may be either naval or commercial. By naval blockade we seek either to prevent an enemy's armed force leaving port, or to make certain it shall be brought to action before it can carry out the ulterior purpose for which it puts to sea. That armed force may be purely naval, or it may consist wholly or in part of a military expedition. If it be purely naval, then our blockade is a method of securing command. If it be purely military, it is a method of exercising command, and as such will be dealt with when we come to consider defence against invasion. But in so far as military expeditions are normally accompanied by a naval escort, operations to prevent their sailing are not purely concerned with the exercise of command. Naval blockade, therefore, may be regarded for practical purposes as a method of securing command and as a function of battle-squadrons. Commercial blockade, on the other hand, is essentially a method of exercising command, and is mainly an affair of cruisers. Its
immediate object is to stop the flow of the enemy's sea-borne trade, whether carried in his own or neutral bottoms, by denying him the use of trade communications.
From the point of view of the conduct of war, therefore, we have two well-defined categories of blockade, naval and commercial. But our classification must go further; for naval blockade itself is equally varied in intention, and must be subdivided. Strictly speaking, the term implies a desire to close the blockaded port and to prevent the enemy putting to sea. But this was not always the intention. As often as not our wish was that he should put to sea that we might bring him to action, and in order to do this, before he could effect his purpose, we had to watch the port with a fleet more or less closely. For this operation there was no special name. Widely as it differed in object from the other, it was also usually called blockade, and Nelson's protest against the consequent confusion of thought is well known. "It is not my intention," he said, "to close-watch Toulon"; and again, "My system is the very contrary of blockading. Every opportunity has been offered the enemy to put to sea." It is desirable, therefore, to adopt terms to distinguish the two forms. "Close" and "open" express the antithesis suggested by Nelson's letter, and the two terms serve well enough to mark the characteristic feature of each operation. Close blockade, it is true, as formerly conceived, is generally regarded as no longer practicable; but the antithetical ideas, which the two forms of blockade connote, can never be eliminated from strategical consideration. It must always be with the relations of these two forms, whatever shape they may take in future, that the strategy of naval blockade is chiefly concerned.
With regard to commercial blockade, in strict analysis it
should be eliminated from an inquiry that concerns methods of securing command and postponed to that section of exercising command which deals with the attack and defence of trade. It is, however, necessary to treat certain of its aspects in conjunction with naval blockade for two reasons: one, that as a rule naval blockade is indissolubly united to a subordinate commercial blockade; and the other, that the commercial form, though its immediate object is the exercise of control, has almost invariably an ulterior object which is concerned with securing control; that is to say, while its immediate object was to keep the enemy's commercial ports closed, its ulterior object was to force his fleet to sea.
Commercial blockade, therefore, has an intimate relation with naval blockade in its open form. We adopt that form when we wish his fleet to put to sea, and commercial blockade is usually the most effective means we have of forcing upon him the movement we leave him free to attempt. By closing his commercial ports we exercise the highest power of injuring him which the command of the sea can give us. We choke the flow of his national activity afloat in the same way that military occupation of his territory chokes it ashore. He must, therefore, either tamely submit to the worst which a naval defeat can inflict upon him, or he must fight to release himself. He may see fit to choose the one course or the other, but in any case we can do no more by naval means alone to force our will upon him.
In the long run a rigorous and uninterrupted blockade is almost sure to exhaust him before it exhausts us, but the end will be far and costly. As a rule, therefore, we have found that where we had a substantial predominance our enemy preferred to submit to commercial blockade in hope that by the chances of war or the development of fresh force he might later on be in a better position to come out into the open. That he should come out and stake the issue in battle was nearly always our wish, and it was obvious that too rigorous
a naval blockade was not the way to achieve the desired end, or to reap the strategical result which we might expect from paralysing his commerce. Consequently where the desire for a decision at sea was not crossed by higher military considerations, as in the case of imminent invasion, or where we ourselves had an important expedition in hand, it was to our interest to incline the enemy's mind towards the bolder choice.
The means was to tempt him with a prospect of success, either by leading him to believe the blockading force was smaller than it was, or by removing it to such a distance as would induce him to attempt to evade it, or both. A leading case of such an open blockade was Nelson's disposition of his fleet off Cadiz when he was seeking to bring Villeneuve to action in 1805. But merely to leave a port open does not fulfil the idea of open blockade, and in this case to opportunity and temptation Nelson added the pressure of a commercial blockade of the adjacent ports in hope of starving Villeneuve into the necessity of taking to the sea.
Finally, in a general comparison of the two forms, we have to observe that close blockade is characteristically a method of securing local and temporary command. Its dominating purpose will usually be to prevent the enemy's fleet acting in a certain area and for a certain purpose. Whereas open blockade, in that it aims at the destruction of an enemy's naval force, is a definite step towards securing permanent command.