This conception of our duty on the sea points directly to the fact that the English fleet must set the standard by which to estimate the necessary size of our naval preparations. A war with England is probably that which we shall first have to fight out by sea; the possibility of victoriously repelling an English attack must be the guiding principle for our naval preparations; and if the English continuously increase their fleet, we must inevitably follow them on the same road, even beyond the limits of our present Naval Estimates. We must not, however, forget that it will not be possible for us for many years to attack on the open sea the far superior English fleet. We may only hope, by the combination of the fleet with the coast fortifications, the airfleet, and the commercial war, to defend ourselves successfully against this our strongest opponent, as was shown in the chapter on the next naval war. The enemy must be wearied out and exhausted by the enforcement of the blockade, and by fighting against all the expedients which we shall employ for the defence of our coast; our fleet, under the protection of these expedients, will continually inflict partial losses on him, and thus gradually we shall be able to challenge him to a pitched battle on the high seas. These are the lines that our preparation for war must follow. A strong coast fortress as a base for our fleet, from which it can easily and at any moment take the offensive, and on which the waves of the hostile superiority can break harmlessly, is the recognized and necessary preliminary condition for this class of war. Without such a trustworthy coast fortress, built with a view to offensive operations, our fleet could be closely blockaded by the enemy, and prevented from any offensive movements. Mines alone cannot close the navigation so effectively that the enemy cannot break through, nor can they keep it open in such a way that we should be able to adopt the offensive under all circumstances. For this purpose permanent works are necessary which command the navigation and allow mines to be placed. I cannot decide the question whether our coast defence, which in the North Sea is concentrated in Heligoland and Borkum, corresponds to these requirements. If it is not so, then our first most serious duty must be to fill up the existing gaps, in order to create an assured base for our naval operations. This is a national duty which we dare not evade, although it demands great sacrifices from us. Even the further development of our fleet, important as that is, would sink into the background as compared with the urgency of this duty, because its only action against the English fleet which holds out any prospect of success presupposes the existence of some such fortress. But the question must be looked at from another aspect.