"They've found something," Darrin chuckled, when he reached the bridge on a call from Lieutenant Fernald. As the "Grigsby" was heading in toward the shoal, and had some minutes still to go, Darrin asked: "Mr. Fernald, you had a second and even more thorough inspection of the hull made, as I directed?" "Yes, sir; and found the hull so secure that I did not wake you to tell you, sir. There has been no strain of the plates sufficient to start any of them." "I'm thankful to hear that," Darrin acknowledged. "Even with the big, elastic cushion of water between us and that awful explosion, it seems almost incredible that we did not wreck ourselves as well as the enemy." "You've found another submarine?" Dave shouted through the megaphone, as he rang for slow speed and ran parallel with the waiting snub-nosed craft. "We've found two somethings, sir," came back the reply. "They lie about four hundred feet apart and heading in the same direction. I can find them again, sir, but I didn't go back over them for fear they'd take the alarm and run for it." "Perhaps they have," Darrin suggested. "I've dropped small buoys, sir, and can lead you over them." "Then do so, and travel at full speed. Be prepared to get out of our way if we come fast after dropping." Even the two cool-headed sailors who stood by the depth bomb apparatus stiffened themselves as they found the "Grigsby" following in the wake of the mine-sweeper. The after lookouts lashed themselves fast against injury by any such surprise as that of the afternoon. As the signal flashed from the mine-sweeper ahead Dave passed the order for the bomb instantly after ordering full speed. There was an explosion, but an ordinary one, such as this crew of the destroyer was accustomed to. At full speed, too, Dave tried for the second hidden enemy boat. There was barely time to have the second bomb in place when signal and order came. Another terrific explosion, like that of the afternoon! It seemed as though the waters must divide! Yet the "Grigsby," moving fast all the time, felt the shock severely, but not like the one of the afternoon. About the destroyer came, playing her searchlight on the waters. The tell-tale oil patches were there, showing only too plainly that two submarine craft had been destroyed. "Apparently one craft carried no mines, while the other was loaded with them," said Dave to his executive officer. "Fernald, I think I'm beginning to get an idea of the way the enemy are working their mine-laying game. If I'm right we'll make a record along this patch of shoals while the hunting lasts." Patiently Fernald listened and waited, but did not speak. He hoped to hear what his chief's idea was, but it was not the executive officer's place to ask for it. "I may even be able to figure out when the best time would be for hunting these lazy rascals resting on the bottom," Darrin continued. Mr. Fernald began to show signs of a more active curiosity.