A depth bomb!  Jack and Ted knew all about the latest device being employed by the warring nations in their campaigns against submarines.  Gigantic grenades, they were, carrying deadly and powerful explosives timed to go off at any desired depth.  One of them dropped from the deck of the destroyer as it passed over the spot where the Dewey had submerged might blow the diminutive ship to atoms.

With reckless abandon big bluff Bill Witt began to sing: 

"It’s a long way to Tipperary, It’s a long way to go.  It’s a long way—–­“

The song was interrupted by a harsh grating sound—–­the crashing of steel against steel—–­and then the Dewey shuddered from stem to stern as though it had run suddenly against a stone wall.

Hurled from his feet by the fearful impact Jack sprawled on the steel floor of the torpedo room.  Ted, standing close by his chum, clutched at one of the reserve torpedoes hanging in the rack in time to prevent himself falling.

For a moment the Dewey appeared to be going down by the stern, with her bow inclined upward at an angle of forty-five degrees.  Above all the din and confusion could be heard the roar of a terrific explosion outside.  The little submersible was caught in the convulsion of the sea until it seemed her seams would be rent and her crew engulfed.

From the engine room Chief Engineer Blaine and his men retreated amidships declaring that the submarine had been dealt a powerful blow directly aft the conning tower on her starboard beam.

“Any plates leaking?” asked Lieutenant McClure quietly.

“Not that we can notice, sir,” replied Blame.  “It appears as though the nose of that Prussian scraped along our deck line abaft the conning tower.”

At any moment the steel plates were likely to cave in under the strain and the submarine be inundated.

“Stand by ready for the emergency valve!” shouted Lieutenant McClure.

This was the ship’s safety contrivance.  The Brighton boys had been wonderfully impressed with it shortly after their first introduction to the “innards” of a submarine.

The safety valve could be set for any desired depth; when the vessel dropped to that depth the ballast tanks were automatically opened and every ounce of water expelled.  As a result the submarine would shoot to the surface.  The older “submarine salts” called the safety the “tripper.”

“If they’ve punctured us we might as well cut loose and take our chances on the surface,” declared Lieutenant McClure to the little group of officers standing with him amidships in the control chamber.

Not a man dissented.  They were content to abide by the word of their chieftain.  It was some relief to know that the nose of the destroyer had not crashed through the skin of the submarine; but, from the concussion astern and Chief Engineer Blaine’s report, it was very evident that the Dewey had been struck a glancing blow.  Deep-sea pressure against a weakened plate could have but one inevitable sequel—–­the rending of the ship’s hull.