The British losses by mine and submarine created some discontent on the ground that our naval strategy was defensive rather than offensive; and military critics, whose notions of naval warfare were derived from the study of German text-books on the principles of war on land, continually pressed for a more active policy, and asked why our superior navy did not treat the German Fleet as the German Army treated its enemies in France and Belgium. It was forgotten that he who possesses all must always be on the defensive; there must be something tangible to attack before there can be an offensive, and there could have been no Trafalgar had Napoleon kept his fleet in harbour. The abandonment of the high seas by the German Navy precluded a naval battle, and the defensive strength of harbour defences which kept Nelson outside Toulon had so increased as to make it vastly harder for Jellicoe to penetrate Wilhelmshaven or Kiel. Naval power, which the war proved to be more than ever effective on sea, was shown to be more than ever powerless on shore. The mine and the submarine made the sustained bombardment of land fortifications a dangerous practice, and moving batteries on shore were more than a match for ships, because they could not be sunk and could be more easily repaired or replaced. There were wild dreams of British forces landing on German coasts, and still wilder alarms about German armies descending on British shores; but the only landing effected on hostile territory during the war was at Gallipoli, and it did not encourage a similar attempt against the better defended lands held by the Germans. We had to content ourselves with the practical realization in war of our continual claim in peace that sea-power is an instrument for the defence of island states rather than one for offence against continental peoples. Only when and where those peoples wished to be defended and opened their ports to their allies, was it found possible to land a relieving force. The British armies which liberated Brussels had to travel via Boulogne and not Ostend; and the German ships which sheltered in port had to be routed out by the pressure of Allied arms on land.