“What are they going to call our new Kaiser-buster?” asked Jack of his chief one morning while they were inspecting the ship’s storage tanks.

“So far as the Germans are concerned she is still the U-91,” said the little captain.  “You notice that we haven’t changed the outside dress of her a single bit.  Unless I lose my guess we are going to get pretty close to the Boche with this old boat of theirs.”

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 fell 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.