instigated by the Central Powers. This, however, due in a measure to the activities of British under-sea craft upon which Jack and Frank had served, had been somewhat lessened lately and German U-boats, as they had come to be known, had not been so active recently.

On land, however, it seemed that neither side had gained much in the last few months. What advantage there was seemed to have rested with the Germans, for the Kaiser’s mighty drive through the Balkans had completely crushed heroic little Serbia and had opened a path to Constantinople for the German hordes. Also it had brought Bulgaria into the war on the side of the Central Powers, giving them the armed weight necessary to keep Greece and Roumania from throwing their support to the Allies, much as they would have liked to do so.

This was the situation, then, when the D-17 steamed slowly toward the German naval fortress of Heligoland.

As Lord Hastings, standing by Frank at the wheel, gave the course, avoiding mines as well as he could by the chart that had somehow come into his possession, Jack retained his place forward in the glass-like cage, his eyes steadily ahead.

For an hour, perhaps, he sat there, seeing nothing that indicated danger.

Then, suddenly, his right hand shot out, his finger touched a little push-button; the throb of the engines ceased as if by magic and the D-17 seemed to halt in her track.

Jack approached Lord Hastings.

“Mine, sir,” he said, quietly.