Fernald, who had been called, having reported, was sent with the chief engineer to make a hull inspection below decks. Though some of the hull plates had been dented inward enough to attract attention, no leak could be found. The "Grigsby" was as seaworthy as ever, though after that rocking shock this seemed a marvel. Off in the distance the "blimp" soon became a mere speck to the watchful eyes of those on the destroyer. Dave directed that the aircraft be followed at cruising speed so long as she remained in sight. When the dirigible was at last lost to view the destroyer lay to, her lookouts using their glasses. "Think the aircraft is coming back, sir," reported a lookout from the military mast. From where he stood on the bridge Darrin could make out nothing for several minutes, though in the interval the lookout aloft reported that he could make out the "blimp" with surety, and that she appeared to be flying a signal, though he could not see what it was. Then from the bridge the "blimp" became visible. A little later, too, the flag signal could be seen and read. "Following another submarine," was what the signal said. Going to starboard of the course Darrin advanced at ordinary speed to meet the "blimp," which, as in the former case, was flying just barely astern of the hidden monster, so that the forward British airman lookout could discern the shape of the craft that was being pursued. Dave waited until the dirigible had passed. He then gave the order, "Full speed ahead," and came about behind the "blimp." Leaping forward the "Grigsby" gave chase, the "blimp" at the same time moving up directly over the intended prey. At the drop of the flag above, Darrin let go his right hand, the signalman transmitted the order, and the bomb rolled overboard. As Dave's hand fell the watch officer advanced the lever of the engine-room telegraph. An extra jump was put into the speed. Again a column of water rose astern, but this time there was only the normal explosion of the depth bomb. "Good hit," said the dirigible, by radio, and the message was called up to the bridge. "Saw her stagger. She's done for." The "blimp" veered off once more, going back over her late course. As the "Grigsby" went about Darrin made out the tell-tale spread of oil on the waves. "This is the real form of hunting," he exclaimed. "Too bad, sir, that none of us thought of it before," remarked Ensign Andrews. "We had to wait and learn," Dave explained. "That's the way that all progress in this war has been registered. We are fighting an ingenious enemy. Destroying the submarine mine-carriers, as we are doing today, won't end the planting of German mines. As soon as the enemy finds out how we are checkmating him he'll invent another scheme, which we'll have to discover before we can beat it." Half an hour later the British aircraft located a third submarine. "A big one, too," she signalled. "Following the same course."