More to the point was the readiness of the merchantman _Valeria_ and of Commander Stockwell's destroyer to turn happy accidents to the best account on the spur of the moment. The _Valeria_ bumped over a rising submarine at three o 'clock one summer morning off the coast of Ireland. Instantly all hands ran to "action stations," when the gunner saw, to his delight, that the periscope had been broken off and so the submarine was blind. His first shot hit the hull. His second was a miss. But his third struck the base of the conning tower; on which the submarine sank, nothing but bubbles and oil remaining to mark the spot where she went down. Stockwell's adventure was rather different. He had marked a submarine slinking round in the early dawn, and, knowing the spot the Germans liked best outside of Liverpool, watched his chance over it. Suddenly he felt his destroyer being lifted up, tilted over, and slid aside. The "sub" had risen right under it! Swinging clear in a moment he let go a depth charge; and the sea-quake that followed had plenty of signs to show that the "sub" had gone down. 1917 was the great year of submarine war: the Germans straining every nerve to kill off all the ships that went to or from the Allied ports, the Allies trying their best to kill off all the submarines. The Mediterranean was bad, the North Atlantic was worse, the west coasts of the British Islands worst of all. The American Navy came in and did splendid service off the south coast of Ireland, in the Bay of Biscay, and along the North Atlantic seaways between French and British and American ports. More and more destroyers were put into service, aided by "chasers"--very much smaller vessels with only one gun and a few men, but so cheap and easily built that they could be turned out in swarms to help in worrying the submarines to death. The "scooters" and "Porte's babies," as we saw in Chapter XXIV, were, however, even better than these swarming "chasers." The enormous steel nets were also used more than ever. You can fancy what they were like by thinking of a gigantic fishing-net many miles long, with armed steamers instead of floats. In the entrances to some harbours there were sea-gates made by swinging open a bit of the net by means of its steamers to let traffic go through, and then swinging it back again. The mine-fields were made bigger than ever; it was then that the vast one, mostly laid by the Americans, was begun from the Orkneys to Norway. Mines were also laid by British submarines and by daring fast surface mine-layers round Heligoland and other places off the German coast. In this way the waters in which submarines could work were made narrower and narrower and were better and better guarded.