ph lever to the engine-room. He
signalled for full speed ahead, then at the proper moment he shouted:

"Let her go!"

An instant later the bomb splashed into the water.

Immediately following the splash there came a sullen, rending roar under
water. A great column of water leaped up from the sea, a heavy volume of
it landing on the after deck of the destroyer, all but washing overboard
one of the lookouts. The pressure of water fairly lifted the stern of the
"Grigsby" until her bow dipped far in.

Ensign Ormsby was thrown flat, almost rolling from the bridge. Dave,
fortunately, had taken a grip that saved him from falling.

It seemed as though the destroyer herself had been blown up, but she
quickly settled and scooted ahead at a furious rate.

"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