."

And then "Little Mack" confided to Jack that the German code book
had been captured with the U-boat, and that, furthermore, the U-91
had shipped as her wireless chief a former secret-service chap, Hal
Bonte, who had worked for a time in the offices of a German-American
steamship line in New York and knew the German language "like a
breeze."

"Of course the U-91 has been re-named," continued the captain. "She
will be known hereafter in the navy department records as the _Monitor_.
You remember what that other _Monitor_ did."

And Jack, of course, recalled at once the famous battle in Hampton
Roads during the Civil War when the little cheesebox of John Ericsson
had whipped the much touted _Merrimac_ after the Confederate terror
had completely dominated the Federal fleet and for a time wrested the
prestige of the sea from the Union.

"Pretty good record to live up to," commented Jack as he recalled the
feats of the famous little Ironsides that had saved the day for the
Union.

"And you bet we'll do it," retaliated his chief.

It was not long before the _Monitor_ was ready to put to sea again.
Thoroughly equipped, her captain and crew familiarized with the
operation of their new craft after a number of trial trips in English
waters, she awaited only the call of duty that would send her forth
for daring exploits against the Hohenzollern navy---a German submarine
born of steel out of the great Krupp works and put together in the
yards at Wilhelmshaven turned against her own sister ships under the
direction of a doughty Yankee crew!

At last came the order to move, an order received with great acclaim
down in the hold of the massive steel structure where her crew of
forty-two men laid wagers on the number of ships they would sink, and
up in the conning tower where her officers fretted to be loose again
in the North Sea. The _Monitor_ carried eight torpedoes and several
tons of shells for her deck guns, while her fuel tanks had enough oil
to keep her afloat for many days.

During the next few weeks the world was startled by the exploits of
some daredevil sort of a submarine that seemed to have an uncanny
habit of turning up right in the heart of German fleets. Units of
the German navy were being sunk with ridiculous ease. U-boat bases
were raided and upon one occasion the mystery submarine had worked
its way into a German harbor and blown up a cruiser.

Late one afternoon, just before dusk, the _Monitor_ fel