s of the three patrol boats report to
me?"

"At once. All three are here in the harbor, and, I am told, they are
ready to put to sea."

"Then, sir, I propose, within a week, to hand you a wholly satisfactory
report," Darrin went on. "I had to put in some time on the ground, and it
was necessary to study a new problem. Then came a series of adventures
that took me out of the work for a while. But now, sir, I hope to show
you something new--results!"

CHAPTER XV

DARRIN SUSPECTS THE GERMAN PLAN

THE three shoals selected by Darrin extended over a length of about
thirty miles along the coast. It was the center one of these shoals on
which he had had previous experience.

Further, it was arranged that Dalzell should, in general, cruise along
the lower fifteen miles of this stretch, while the "Grigsby" should cover
the upper half. From time to time the two destroyers would meet.

After sending three mine-sweepers and the three patrol boats to the
shoals, two craft to each shoal, Darrin saw to it that the other six were
assigned to duty in the deeper waters off shore.

Then, with a hearty signal to the "Reed," the "Grigsby" started
northward. She steamed by the southernmost shoal, and was passing the
second when Darrin was called to the bridge by Ensign Ormsby.

"That patrol boat in there signals that she has made a find, sir, so I
have changed the course and am heading in."

Dave's eyes gleamed as he made out the next signal from the patrol, which
was:

"Soundings show her to be a big craft. Shall we rig the small bombs on
the sweep wires?"

"Wait until we arrive," was the answering signal from the "Grigsby."

In a few minutes the destroyer was within hailing distance of the patrol
boat, which was lying to in the neighborhood of the find.

"The enemy submarine appears to be at least 275 feet long, sir," reported
the patrol boat commander.

"Then a depth bomb should do the business better," Dave shouted back
through the megaphone. "Sail over the craft with your sweep, and I'll
follow. Signal when you judge us to be squarely over her."

Under bare headway the "Grigsby" fell in behind the now slow-moving
patrol boat. Almost at once the wire sweeps discovered the hull of the
hiding monster.

Ahead steamed the patrol boat, the destroyer following. Aft two men stood
by the depth bomb apparatus. Down came the white flag of the British
signalman on the smaller craft.

Dave's hand rested on the telegra