"Half speed ahead," Darrin signalled, as soon as he could let go his grip, and the "Grigsby" slowed down. At the same time she swung around.
Even at that distance the huge spread of oil on the surface could be seen. A wild Yankee cheer rose, which was promptly echoed by the British tars of the patrol boat.
"No depth bomb ever made that upheaval," Dave gasped, as soon as he could speak, and Mr. Ormsby, much shaken, had picked himself up. "The bombs are ugly affairs, but that felt like the explosion of about ten of them."
"Did you notice, sir, that the explosion lasted more than twice as long as we"ve ever known one to last before?" the watch officer asked.
"Yes."
"Then what happened, sir?"
"Either our explosion touched off a torpedo, which does not seem likely, or else--"
For an instant what he was about to say sounded so absurd that Darrin hesitated.
"Well, sir--?" queried Ormsby.
"Or else that was a mine-layer, with a full cargo of mines aboard, all ready for business, and--But you"ll think I"ve gone daffy."
"No, I won"t, sir; not after the way this ship rose out of the water,"
the watch officer declared. "You mean, sir, that our bomb went off right over that craft"s cargo of mines, and that the shock must have set off the mines."
"That"s certainly the way it looks to me," Darrin nodded.
"I believe it, sir."
Just a few moments later the patrol boat came within hail. Through his megaphone Darrin stated what he believed had taken place.
"It"s the only thing to account, sir, for such a tremendous explosion,"
replied the commander of the patrol. "I"ve been on hand to see a lot of depth bombs go off, and I never saw an upheaval like the one you produced, sir."
"Have soundings taken, Mr. Ormsby," Darrin directed. The depth of the water was quickly reported. Dave glanced at the sky.
"The light will be strong enough for another hour," he decided. "Have our two divers prepare to go down at once."
A launch, cleared away with the divers on board, was anch.o.r.ed in the middle of the oil spot. Two divers went over the side. Presently they signalled for extra cables. When these were let down they attached pieces of metal and gave the signal to haul away.
By the time that the hour was up Darrin had abundant evidence to prove that he had destroyed a mine-layer, and that his bomb had blown up several mines stored on the craft. This evidence took the form of fragments of mines.
"Some of these pieces must even have been driven up against our hull,"
Darrin declared. "It is a wonder that we were not sunk."
"The counter pressure of the water would lessen the force of these fragments, especially after they had been blown out through the sh.e.l.l of the submarine," Lieutenant Fernald argued. "But I agree with you, sir, that it"s a wonder the "Grigsby" suffered nothing worse than a shaking."
Other evidence, too, the divers sent up. The destroyed craft had surely been a mine-laying submarine. The divers measured the length of the wrecked hull, finding it to be close to three hundred feet. They reported, too, that scores of German dead lay in the wreckage.
For hours nothing more happened. Just before ten o"clock that night the mine-sweeper"s blinkers signalled a call to the "Grigsby," then about four miles distant.
"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 pa.s.sed 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.
"But I won"t say much about it," Darrin smiled, "until I"ve more data to work on and have proved some part of my theory."
Lieutenant Fernald looked so much like a man who wished to speak that Dave laughed.
"Out with it, Fernald," he urged good-humoredly. "You"ve an idea, too.
You may tell me if you wish."
"Why, sir," replied the executive officer, "I"ve about concluded that the enemy mine-laying submarines do not go back to base port for more mines.
They have some method for delivering them near here, and thus the mine-layers are able to keep more steadily at work."