puzzled.

"There probably is a canal near at hand that the Germans have dug out
since their occupation of Belgium, and which they now are using as a
retreat for their light draft vessels---possibly a submarine base,"
answered McClure.

For a time the _Dewey_ followed steadily on in the wake of the German.
It was not long until McClure, at the forward periscope, was able to
get a better look at the foe.

"A big destroyer," he announced. "I can make out her four funnels."

It was now apparent to the lieutenant that they were approaching close
to the coast and that very shortly the destroyer must turn again to
the sea or else take her way into some tortuous channel leading inland.

"Reckon we have gone as far as we can," he declared after a further
observation. He had in mind the fact that the approach to the waterway
for which the destroyer was headed most certainly was mined and
that without a chart of the course he was running the risk of driving
into one of the dangerous buoys.

He determined to chance a shot at the destroyer, submerge and go out
to sea again. Sighting on the dimly outlined destroyer he released
a torpedo and then, without waiting to observe the result of the
random shot, gave the signal to dive.

Down went the _Dewey_. And in another moment, as the gallant sub
slipped away into the depths, she lurched suddenly with a staggering
motion and brought up sharp with an impact that shook the vessel from
stem to stern. Officer Cleary was catapulted off his feet and crashed
into the steel conning tower wall, with an exclamation of pain.
The _Dewey_ seemed to have run hard against an undersea wall.

"Reverse the engine!" shouted McClure. "We must have run upon a
sandy shoal."

Frantically he rang the engine room to back away. But the order came
too late. With a slow ringing noise that plainly bespoke the grating
of the ship's keel on the bed of the ocean the submarine slid forward
and then came to a dead stop, quivering in every steel plate from the
tremendous throbbing of her engines.

"Great Scott, we've run aground!" exclaimed McClure as he stood
wild-eyed in the conning tower.

Jack was despatched to the engine room for a report from Chief Engineer
Blaine. He returned in a moment to say that the ship's engines were
reversed and the propeller shafts revolving to the limit of the
ship's power. Nevertheless, it was only too evident that the _Dewey_
was enmeshed in a treacherous shoal fr