All these mechanical developments of the Fleet, which are so essential at the present time, grew out of the impetus given in and after the year 1904. But that was not the only thing which placed the country in such a position of advantage at the beginning of the war. The battle-fleet and cruiser squadrons had been reorganised to coincide with the needs of the Empire, owing to the shifting of the stress of naval power from the Atlantic and the Channel to the North Sea. Some squadrons in distant waters were reduced in strength to correspond with the requirements, and non-fighting ships—vessels too weak to fight and too slow to run away—were brought home from distant seas, and their officers and men were made available for modern ships. A system of nucleus crews was adopted for the reserve ships to facilitate mobilisation and to make sure that the ships would be really fit for sea. Before that time the whole Fleet had been pivoted on the Mediterranean, and a British warship was rarely seen in the North Sea. By progressive steps the naval front was changed from the South to the East. On the east coast of the United Kingdom destroyer and submarine flotillas were based on ports prepared for them. A great dockyard was erected at Rosyth, and all along the coast naval bases were developed, and every preparation was made for the possibility of war. These were developments of great significance, and the immense and growing strength of the British Fleet justified the French in concentrating their battle squadrons in the Mediterranean, and leaving at Brest and in the Channel only a division of cruisers, supported by flotillas. Fleets of warships are meant to fight when the need for fighting comes; but there was no affront to Germany, no cause for resentment or agitation, in the concentration of the main strength of the British Fleet in such places, and with such bases, that they could carry their power into the North Sea. Force attracts force in strategy as in physics, and the growth of the German High Sea Fleet at Wilhelmshaven, with the great sea canal thence to Kiel on the Baltic, inevitably brought about the British concentration. How magnificently advantageous was the position secured has already been shown. In an earlier chapter it has also been explained that by the strategic position occupied by the Grand Fleet, and the grip held on the entrance to the Channel at Dover, the North Sea became strategically a closed sea—a _mare clausum_.