JACK TURNED HIS WHIP FROM THE BACKS OF THE HORSES AND LASHED OUT AT THE WOLVES.

“Submerge to five fathoms, Mr. Templeton!”

The speaker was Lord Hastings, commander of the British submarine D-17.

Jack Templeton, a British youth and first officer of the under-sea craft, repeated the command for which he had been waiting now for some moments.

“Mr. Chadwick!”

Lord Hastings’ voice again.

“Sir!”

A third figure, standing upon the bridge—now enclosed as the submarine sank from the surface—came to attention before his commander. Frank Chadwick, an American youth and second officer of the vessel, awaited instructions.

“Everything shipshape?” questioned his commander sharply.

“Yes, sir. Engine-room trouble all repaired, sir.”

“Lookout posted forward?”

“Yes, sir!”

“Very well. Ten fathoms, Mr. Templeton!”

Lord Hastings turned from the periscope, through which he had been peering, and for a moment gazed thoughtfully at his two young officers before speaking. At last he said:

“Unless something goes wrong we will be in Heligoland within two hours!”

A startling statement, this, to one who did not know the nature of the man who made it; for it was a fact known to all the world that Heligoland, the great German fortress that guarded the approach to the few miles of German seacoast, was one of the strongest in the world—perhaps as well fortified as Gibraltar itself, and considered by naval experts equally as impregnable.

Apparently the D-17 was bent upon a perilous venture.

Such, indeed, was the case. The D-17, sister ship to the D-16, in which Lord Hastings and his two young officers had seen many exciting adventures, as related in “The Boy Allies with the Terror of the Seas,” had left the coast of England the day before, heading straight for the strongly fortified German base; and now she was almost there.

Just what