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.