Then had followed months of excitement and adventure. They had taken part in British successes and reverses on all the seven seas. They had been "in at the death" in the first British naval victory off Heligoland; they had followed the German cruiser _Emden_, "the Terror of the Sea"; they had been in action with the British fleet that destroyed the German squadron off the Falkland Islands in the western hemisphere; they had seen action in other parts of the globe--at the Dardanelles, with the Japanese at Tsingchau, with the French in the Adriatic and with the Russians in the Baltic. In a word, they were veterans. Many were the narrow escapes they had had, but they had always survived. Their latest venture had almost cost Frank his life, for, after the submarine upon which they sailed had been destroyed, Frank engaged in a death struggle with a British traitor in the waters of the North Sea and had won by a scant fraction. He was unconscious when rescued by his chum and he had remained inactive, as had the others, in England for several weeks. But now, the D-17 having been put in service, Lord Hastings had been named to command her and all were eager to get busy again. Frank, though sturdy and strong, was by no means a match for his chum, a powerful and husky young Englishman. Also he was naturally more hot-headed than his friend, and given to taking foolhardy chances--at times. Jack's coolness had saved both more than once. Jack was what Frank called a real fighter and had proved his mettle more than once since the two had been together. Strong as an ox, he was a bad customer to tackle in a rough and tumble and he was exceedingly proficient in the use of his fists. Also he was a fair swordsman and a fair shot. It was in the latter accomplishment that Frank excelled. He was a dead shot with either rifle or revolver, as he had proved in several tight situations where straight shooting had been necessary. He had never failed in this respect. Fortunately, both lads spoke German and French as well as English, and under Lord Hastings' tutoring, they had also picked up a smattering of Italian, Russian and Hungarian--not much, perhaps, but enough to carry on a conversation, although with some difficulty. At the time the D-17 made her way toward Heligoland, the great war was almost at a standstill. It seemed that the warring nations had reached a deadlock that could not be broken. On sea, of course, the Allies held the whip hand, except for the submarine warfare 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.