The German High Command realised this as quickly as that of the Allies. Their oversea commerce was strangled within a few days of the Declaration of War with Great Britain, and their fleet was confined to harbour, with the exception of occasional operations against Russia in the Baltic. From the German standpoint the naval problem resolved itself into one of how best to strike at the lines of communication of the Allies, paying special attention, first, to the transport of troops, and, second, to England's food supply. As they alone knew to what extent they would violate the laws of war and of humanity, it became apparent that the submarine and the mine were the only possible weapons which could be used for this purpose in face of the superior fleets of the Allies. But the number of these weapons was strictly limited compared with the immense shipping resources at the command of the Western Powers, so one submarine must do the work of many, and an effort was made to accomplish this by a reign of sea terrorism and inhuman conduct unparalleled in the history of the world. It opened with the sinking of the _Lusitania_. The Allies had secured and maintained the command of the sea, and _all that it implies_, but to do this with the certainty of correct strategy they had to dedicate almost their entire battle fleet to the purpose for which battle fleets have always been intended--the checkmating or annihilation of the opposing navy. There came a second problem, however, one entirely new to sea warfare, and unconsidered or provided against in its strategic and tactical entirety because hitherto deemed too inhuman for modern war. This was the ruthless use of armed submarines against unarmed passenger and merchant ships, and the scattering broadcast over the seas, regardless of the lives and property of neutrals, of thousands of explosive mines. The type of ship constructed exclusively for open sea warfare against surface adversaries was not the best answer to the submarine. The blockading of the hostile surface fleet did not prevent, or even greatly hinder, the free passage of submarine flotillas, and the building by Germany of under-water mine-layers enabled fields of these weapons to be laid anywhere within the carrier's radius of action. In this way the second, or submarine, phase of the naval war opened, and it was to supplement the comparatively few fast destroyers and other suitable ships which could be spared from the main fleets that the "new navy" was formed. THE SHIPS