Another half hour passed, for, though the dirigible moved swiftly, the underseas craft she was watching was moving only at submerged speed. Then the chase led on past the "Grigsby." Purposely Darrin allowed it to go by him by about a mile ere he joined in the pursuit. Starting at half speed ahead he soon changed it to full speed. And now the dirigible had slowed down, until she was travelling, as her signals stated, at just the speed of the submerged craft directly under her. "We'll go in by the stern and try to make a quick job of it," Darrin proposed, as he gave Andrews final instructions, and turned to see that the signalman with his flag stood well aft on the superstructure. As the destroyer raced in almost under the dirigible Darrin raised his right hand. The signalman with the flag did the same. Just as the "Grigsby's" bridge passed in under the tail of the aircraft Dave Darrin read the signal for which he had waited. The airmen were telling him that the bridge of his craft was almost over the bow of the hidden enemy beneath. Down came Dave's raised hand. Seeing it fall, the signalman let his flag drop. In that same instant the depth bomb was released for its course over the "Grigsby's" stern. Almost in the same second there sounded a terrific if muffled report under the surface. The water rose in three distinct columns, lifting the stern of the "Grigsby" and almost burying her bow under. It was as though a great geyser and an earthquake had met. Columns like waterspouts hurled themselves across and over the reeling destroyer. Even when the "Grigsby's" nose came out and up once more the destroyer rocked in the near tidal wave that the swift series of explosions had produced. "Pardon me, sir," begged Ensign Andrews, when he had regained control of himself. "I feel constrained to remark, sir, that you appear to know how to get all the thrills out of life." "We must have landed right over a mine cargo once more," Dave answered smiling. "There were several explosions, but they came nearly together. One of these days we'll start something like that that will send us up half a mile into the air. But it's great sport, Andrews, especially when you pause to think what it all means." "Great sport for us, but too sudden for the Huns," rejoined the watch officer. "They cannot have had the satisfaction, even, of realizing that anything had hit them." Satisfied that there would be no more underseas explosions, Darrin gave the order to come about. That the underseas craft had been struck was indicated clearly enough by the patches of oil on the water. The force of the explosion told the Yankee tars that the craft must have been blown into bits. "Best thing I ever saw done!" signalled the British officer in command of the "blimp." "Find us another, and we'll try to show you something just as good," Darrin caused to be signalled back.