In stature and disposition the boys were as different as could be. Frank, though large for his age, looked small when alongside of Jack. The latter, though no older than his friend, was a huge bulk of a boy, standing well over six feet. He was built proportionately. Strong as an ox, he was, and cool of head. Here he differed from Frank, who had something of a temper and was likely to do something foolish on the spur of the moment if he became angry. Jack had served as a damper for his friend's anger and enthusiasm more than once. That they could fight, both boys had shown more than once. Jack, because of his huge bulk and great strength, was, of course, harder to beat in a hand-to-hand struggle than was Frank; but what the latter lacked in this kind of fighting, he more than made up in the use of revolver, rifle or sword. Frank was a crack shot with a revolver; and more than once this accomplishment had stood them both in good stead. Each was a good linguist and conversed in French and German as well as in English. This also had been of help to them in several ticklish situations. On their last venture, at which time they had been under command of Lord Hastings, they had reached the distant shores of Russia, where they had been of some assistance to the Czar. In reaching Petrograd it had been necessary for them to pass through the Kiel canal, which they had done safely in their submarine in spite of the German warships and harbor defenses. Also they had managed to sink several enemy vessels there. Returning, Frank and Jack had gone home with Lord Hastings, where Lady Hastings had insisted that they remain quiet for some time. This they had done and had been glad of the rest. One day Lord Hastings had come home with the announcement that he had been called back into the diplomatic service. It was the aim of the British government to align Greece and Roumania on the side of the Allies. Realizing that they could not hope to accompany Lord Hastings, and not wishing to remain idle longer, Frank and Jack had requested Lord Hastings to have them assigned on active duty at once. Lord Hastings promised to do his best. And this was the reason that Frank Chadwick and Jack Templeton found themselves aboard H.M.S. _Queen Mary_ when she steamed out to the North Sea on an evening in the last week of May, 1916. CHAPTER II A BIT OF HISTORY Up to this time the German Sea fleet, as a unit, had suffered comparatively little damage in the great war. Sheltered as it was behind the great fortress of Heligoland, the British sea forces had been unable to reach it; nor would the Germans venture forth to give battle to the English, in spite of the bait that more than once had been placed just outside the mine fields that guarded the approach to the great German fortress itself.