This command came at the top of the voice, for concealment was now no longer necessary. In a twinkling up went the battle flag, bulwarks fell down, lifeboats on decks collapsed, revealing guns, sides dropped from deckhouses, hen-coops, and other innocent-looking structures. The apparently sinking merchantman became a volcano of smoke and fire; scores of shells dropped upon the submarine, punching holes in her frail hull, hurling German sailors high into the air, sometimes decapitating them or blowing off their arms or legs. The whole horrible scene lasted only a few seconds before the helpless vessel would take its final plunge to the depths, leaving perhaps two or three survivors, a mass of oil and wood, and still more ghastly wreckage, to mark the spot where another German submarine had paid the penalty of its crimes. IV It was entirely characteristic of this strange war that the greatest exploit of any of the mystery ships was in one sense a failure--that is, it did not succeed in destroying the submarine which attacked it. On an August day in 1917 the British "merchant steamer" _Dunraven_ was zigzagging across the Bay of Biscay. Even to the expert eye she was a heavily laden cargo vessel bound for Gibraltar and the Mediterranean, probably carrying supplies to the severely pressed Allies in Italy and the East. On her stern a 2-½ pounder gun, clearly visible to all observers, helped to emphasize this impression. Yet the apparently innocent _Dunraven_ was a far more serious enemy to the submarine than appeared on the surface. The mere fact that the commander was not an experienced merchant salt, but Captain Gordon Campbell, of the Royal Navy, in itself would have made the _Dunraven_ an object of terror to any lurking submarine, for Captain Campbell's name was a familiar one to the Germans by this time. Yet it would have taken a careful investigation to detect in the rough and unkempt figure of Captain Campbell any resemblance to an officer of the British navy, or to identify the untidy seamen as regularly enrolled British sailors. The armament of the _Dunraven_, could one have detected it, would have provided the greatest surprises. This vessel represented the final perfection of the mystery ship. Though seemingly a harmless tramp she carried a number of guns, also two torpedo tubes, and several depth charges; but even from her deck nothing was visible except the usual merchant gun aft. The stern of the _Dunraven_ was a veritable arsenal. Besides the guns and depth charges, the magazine and shell-rooms were concealed there; on each side of the ship a masked torpedo tube held its missile ready for a chance shot at a submarine; and the forward deck contained other armament. Such was the _Dunraven_, ploughing her way along, quietly and indifferently, even when, as on this August morning, a submarine was lying on the horizon, planning to make her its prey.