Our title "Submarining" means any kind of underwater attack, by mines as well as by torpedoes, so we must take a glance at the mines before coming to the submarines. Most mines are somewhat like big buoys with little horns all over the top. Each horn ends in a cap which, when hit, sets off the charge. Mines coupled together by a steel rope are more dangerous than two separate mines would be, as they are bound to be drawn in against any ship that strikes any part of the rope. The only safeguard a ship could carry was a paravane. A paravane is made up of a strong steel hawser (rope) that serves as a fender, and of two razor-edged blades that serve to cut the mine-moorings free. It is altogether under water and is shaped like a V, with the point jutting out on the end of steel struts ahead of the bows, the two strokes running clear of the sides, and their ends well winged out astern, where the two sharp blades stand straight up, one from each end. The lines by which mines are anchored were thus guided clear of the ship till they reached the blades, where they were cut. The mines then rose to the surface, where they could be set off at a safe distance. Dragging a paravane through the water made the ship go slow. But that was better than being blown up. Minefields cannot, of course, be crossed at all. You might as well try to walk over armies of porcupines in your bare feet. Some minefields were very big. One British field ran from the Orkneys right across to Norway, to stop the German submarines from getting out round the north of Scotland. The American Navy did magnificent work at this field, the greater part of which was laid by American, not by British, vessels at the latter end of 1917 and earlier part of 1918. Other minefields blocked the Channel. But here the Germans once played a very clever trick which might have cost the British dear. A British minefield had been laid, some fifty feet deep, to catch submarines without being in the way of vessels on the surface. Two days after it had been secretly laid at night the _Nubian_, a British destroyer, had her bows blown off on the very same spot. The German submarine mine-layers had crept in by night and laid a shallow German minefield, exactly over the deep British minefield, to catch those who were trying to catch them. That, however, is not the end of the story. Just after the _Nubian_ had been towed into Portsmouth with her bows blown off, the _Zulu_, a destroyer of the same class, was towed in with her stern blown off. So perfectly were both these vessels built that, when they had each been cut in half, the good halves made an absolutely perfect new destroyer, which, under her compound name of _Zubian_, did excellent work against the Germans during the famous fights at Zeebrugge and Ostend.