l in with a
submarine of unusual length and depth, a monster vessel of the type
of the famous _Deutschland_ that had made the memorable transatlantic
voyage earlier in the war, but of even greater displacement.

Running partly submerged the _Monitor_ had sighted the big fellow
several miles astern. Jack was in the conning tower at the wheel
when he noticed the U-boat across the water.

"Looks like an undersea cargo boat," said Jack after he had reported
to McClure, and the two stood gazing intently at it through the
periscopes.

"The Germans aren't trading with cross-atlantic nations any more,"
said "Little Mack" with a grim smile. "Most likely she is a mother
ship for submarines. She has her wireless antenna up and is talking
to some one. Suppose we go above and get in communication with her."

Accordingly, the engines were slowed down and the _Monitor_ ascended
until she was awash. In that position her wireless aerials,
telescopically arranged like her periscopes, were run out and the
wires strung.

Almost immediately she "cut in" on the big submersible.

At that moment the latter vessel spoke the _Monitor_ and wanted to
know who she was.

"Tell him the U-108 out of Zeebrugge," the American skipper told his
wireless chief.

The message, in German code, was clicked out by Hal Bonte.

For a few minutes the two ships flung their wave lengths at each other
and then the _Monitor's_ operator closed the key to say to his chief:

"That chap over there is the _Bergerhof_, mother ship of the German
U-boat fleet with supplies of fuel and food for our enemy's submarines.
She is keeping a tryst here with her children and expects them at
this rendezvous within the next two hours. After which the well-filled
children are to visit the English channel and attack a group of
transports scheduled for convoy to France the following night. She
signals us to heave to and wait the appointed time."

McClure chuckled at the announcement.

"Just as I thought. Give them an O.K. in your best German," was his
rejoinder.

CHAPTER XXI

TRAPPED

Gain the _Monitor_ spoke the _Bergerhof_ and received in turn a summons
to come alongside and take on fresh stores of fuel.

"If we do we will disclose our identity and it will be all off," said
"Little Mack" in a quandary.

Then Jack had an inspiration.

"Tell them we are having some trouble with our diving rudders and will
be along shortly," he offered.

"Little M