Of speedy victory let no man doubt, Our worst work’s past, now we have found them out. Behold, their navy does at anchor lie, And they are ours, for now they cannot fly. _Andrew Marvel_, 1653. Of all the theatres of the war, on sea or land, the North Sea is the most important. It is vital to all the operations of the Allies. Command of its waters and its outlets is the thing that matters most. In that sea is the centre of naval influence. It is the key of all the hostilities. From either side of it the great protagonists in the struggle look at one another. There the great constriction of the blockade is exerted upon Germany. It is the _mare clausum_ against which she protests. Geography is there in the scales against her. She rebels against British sea supremacy. The “freedom of the seas” is, therefore, her claim—though she is endeavouring to qualify to be the tyrant of them. Her only outlook towards the outer seas is from the Bight of Heligoland and the fringe of coast behind the East Frisian Islands, or from the Baltic, if her ships pass the Sound or the Belt, issuing into the North Sea through the Skager-Rak. But they cannot reach the ocean, except through the North Passage, where the Grand Fleet holds the guard. Only isolated raiders, bent upon predatory enterprise, have stealthily gone that way after nightfall. At the southern gate of the North Sea, through the Straits of Dover and in the Channel, the way is barred. The guns of Dover, the Dover Patrol, and certain other deterrents forbid the enemy to adventure in that direction. [A] See Map I., at end of book. The new engines of naval warfare—the mine, submarine, airship, and aeroplane—found their first and greatest use in the North Sea; and only by employing craft which hide beneath the water, and, on rare occasion, by destroyers which seek the cover of darkness for local forays, have the Germans been able to exert their efforts in any waters outside the North Sea. At the beginning of the war they had raiding cruisers in the Pacific and Atlantic, and a detached squadron in the Far East; but the British Fleet reached out to those regions, and, aided by the warships of Japan and France, it drove every vestige of German naval power from the oceans.