erhead.

Suddenly the messenger's startled voice roared out the message passed by
the radio operator:

"_Full speed astern!_"

In the same instant Lieutenant Fernald repeated the order over the
engine-room telegraph. There was a jolting jar as the "Grigsby"
shivered, then glided back in her own wake.

"Jove! That was a narrow squeak!" came down from the sky. "That hornet
laid an egg in your path. It came within an ace of bumping your keel."

"Never did speed pay a prompter profit, then," uttered Darrin, his cheeks
paling slightly.

For the Englishman's laconic message meant that the submarine had just
proved herself to be of the mine-laying variety. Further, the Hun craft,
hearing the destroyer's propellers almost overhead, had judged the moment
at which to let loose a mine, which, rising to its proper level under
water, would have struck the hull of the advancing destroyer.

Had that happened, the career of the "Grigsby" would have been over, and
several officers' and seamen's names would have been added to the war's
list of dead.

"Going to try again, sir?" asked Lieutenant Fernald, quietly, as Dave
himself changed the full-speed-astern order.

"It's out of our line, I guess," Darrin confessed, with a smile. "Signal
yonder mine-sweeper to close in on the job."

As a result of the message, and aided by the "blimp" overhead, the
snub-nosed mine-sweeper steamed into position. First, her wire sweeper
picked up the mine that had been sprung for the "Grigsby's" undoing, and
backed away.

Then, under Dave's further order, after the mine had been hoisted on
board, the snub-nosed craft moved in with a different type of sweeper. To
different wires of this implement were attached small but powerful
contact bombs. Jauntily the snub-nosed craft moved over the lurking place
of the submarine, and passed on ahead.

From the depths came muffled sounds, followed by a big and growing spread
of oil on the water.

"Enemy done for!" signalled the "blimp."

"Thank you, sir. We know it," the "Grigsby" wirelessed back.

The mine-sweeper, having passed on ahead, now circled back, her crew
grinning at sight of the mass of floating oil.

The contact bombs dangling from the sweep wires had struck against the
submarine's hull and exploded, letting in the water at several points.
The Hun seamen were even now drowning, caught without a show for their
lives, just as they had probably sent many souls to graves in the ocean.

For