“Just tell us what you want, Mr. Benson,” proposed Cadet Merriam, amiably.

“This fellow has been ‘doping’ our engines,” announced Captain Jack.  “And now he’s threatening to stand us off.  We’ll close in on him from both sides.  If he tries to use that steel bar on any of us—­”

“If he does, he’ll curse his unlucky star,” declared Midshipman Merriam.  “Come on, gentlemen.  We’ll show him some of the Navy football tactics!”

The three midshipmen approached Truax steadily from the right.  Jack, Hal and Williamson stepped in on the left.

With a yell like that of a maniac Sam Truax swung the bar.

Having to watch both sides at once, however, he made a fizzle of it.  The bar came down, but struck the floor.

Then, with a yell, the midshipmen leaped in on one side, Jack leading the submarine forces on the other.  Mr. Merriam’s trip and Jack’s smashing blow with the fist brought Truax down to the floor in a heap.

“Now, cart this human rubbish out of here!” ordered Jack Benson, sternly.  “Don’t hit him—­he isn’t man enough to be worthy of a blow!”

Swooping down upon the prostrate one, Hal and the midshipmen seized Sam Truax by his arms and legs, carrying him bodily out of the engine room.

“Williamson,” commanded Captain Jack, “stop the speed.”

“In the race, sir.  We—­”

“Stop the speed,” repeated Benson.

“You’re the captain,” admitted Williamson.  Grasping the twin levers of the two motors he swung them backward.

“Disregard any signal to go ahead until we’ve had a chance to inspect the motors,” added Captain Jack.

Then the submarine skipper darted out into the cabin.

Sam Truax lay sprawling on the floor.  Midshipman Merriam, a most cheerful smile on his face, sat across the fellow, while Hal and the other two midshipmen stood by, looking on.

“Hold him please, until I can have the wretch taken care of,” requested Captain Jack, making for the spiral stairway to the conning tower.

Just as the young skipper stepped out on deck he heard the “Hudson’s” bow-gun break out sharply in the halting signal.

Taking a megaphone, Benson stood at the rail until the gunboat ranged up alongside.

“Have you broken down?” came the hail from the gunboat’s bridge.

“I thought it best to stop speed, sir.  We’ll have to look over our engines before it will be safe to attempt any more speed work,” Captain Jack answered.  “I’ve caught a fellow tampering with our machinery.  We hold him a prisoner, now.  Can you take him off our hands, sir?”

“One of your own men?” came back the question.

“Of course, sir.”

“We’ll send a marine guard to take him, on your complaint, Mr. Benson.”

“Thank you, sir.”

The gunboat’s engines slowed down.  Ere long her port side gangway was lowered.  Jack saw not only two marines and a corporal come down over the side, but Lieutenant Commander Mayhew appeared in person.  That officer came over in the cutter.