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 Mack” seized upon the suggestion and acted promptly.  In code the mother submarine answered that she was coming to aid.  “Let her come; we’ll give her a hot reception,” said McClure grimly.

As the Bergerhof neared them McClure submerged a little and jockeyed his vessel into position for a sure shot.

This aroused the suspicions of the German and she asked whether the steering apparatus of the U-los had again gone wrong.

“Here is our answer,” exclaimed McClure, and catching the big submersible full on the sight of the periscope glass, he released a torpedo.