What, then, do we mean by naval defence? To arrive at a right answer we must first clear our mind of all confusing shadows cast by the accidents of land defence. Both on land and at sea defence means of course taking certain measures to defer a decision until military or political developments so far redress the balance of strength that we are able to pass to the offensive. In the operations of armies the most usual means employed are the holding of positions and forcing our superior enemy to exhaust his strength in attacking them. Consequently the idea of military defence is dominated by the conception of entrenched positions and fortresses.
In naval warfare this is not so. At sea the main conception is avoiding decisive action by strategical or tactical activity, so as to keep our fleet in being till the situation develops in our favour. In the golden age of our navy the keynote of naval defence was mobility, not rest. The idea was to dispute the control by harassing operations, to exercise control at any place or at any moment as we saw a chance, and to prevent the enemy exercising control in spite of his superiority by continually occupying his attention. The idea of mere resistance was hardly present at all. Everything was counterattack, whether upon the enemy's force or his maritime communications. On land, of course, such methods of defence are also well known, but they belong much more to guerilla warfare than to regular operations. In regular warfare with standing armies, however brilliantly harassing operations and counter-attack are used, the fundamental conception is the defended or defensible position.
Similarly at sea, although the essence of defence is mobility and an untiring aggressive spirit rather than rest and resistance, yet there also defended and defensible positions are not excluded. But they are only used in the last resort. A fleet may retire temporarily into waters difficult of access, where it can only be attacked at great risk, or into a fortified base, where it is practically removed from the board and cannot be attacked at all by a fleet alone. But the occasions on which such expedients can be used at sea are far rarer than on land. Indeed except for the most temporary purposes they can scarcely be regarded as admissible at sea, however great their value on land. The reason is simple. A fleet withdrawing to such a position leaves open to the enemy the ulterior object, which is the control of sea communications, whereas on land an army in a good position may even for a prolonged period cover the ulterior object, which is usually territory. An army in position, moreover, is always doing something to exhaust its opponent and redress the unfavourable balance, but a fleet in inactivity is too often permitting the enemy to carry on operations which tend to exhaust the resources of its own country.