o make sure
that I understand just what you propose to do."

On the map Darrin traced the course that he felt sure the German
underseas craft pursued when bringing cargoes of mines to the other
submarines that were laying mines in British waters.

"That would be the natural course for such craft to take," agreed Admiral
Wheatleigh. "I trust that you are right in your surmises. If you are, we
should have some excellent results within the next few days."

"I shall know, sir, within forty-eight hours, and I think it likely that
the enemy will also hear something about it within the next few days. At
least, sir, the German admiralty should be able to guess."

Dave took his leave, hastening back to the "Grigsby," which, an hour
later, weighed anchor and stood out to sea. By that time Dave was sound
asleep, for he had been through a great deal and was sorely in need of
rest before he reached the scene of his intended activities.

Some hours later he was called, and was soon on the bridge.

"You are at the point at which you wished to be called," said Fernald
when Dave reached the bridge.

"And you will do well to seek your own rest now, Mr. Fernald," Darrin
answered. "You can be called, if needed."

Half an hour later Darrin made out, in the sky astern, a tiny speck that
rapidly came closer, and proved to be the dirigible sent at his request.

As the dirigible came nearer signals were rapidly exchanged. The course
for the aircraft was made plain. As for the "Grigsby," her speed was
slowed down to mere headway and she loafed over the waters.

Two hours passed during which the "blimp" aloft sailed rapidly to and fro
in the sky, zig-zagging over the course in a way that covered several
square miles in an hour.

"She's found something, sir!" cried Ensign Andrews.

"She has sighted a craft, bound over the course we had suspected," said
Darrin, as signals broke out rapidly from the car under the big gas bag.
"We'll let the submarine get by us before we start in chase."

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 submerg