Not another sound, and even these only audible to the men who had launched the torpedoes, and two powerful engines of destruction, aimed true, sped on the errand of death and disaster. At the same moment the signal board flashed: "Submerge!" CHAPTER IV. A DARING PLAN. Jack stepped to Lord Hastings' side and shouted: "Did we get 'em?" Lord Hastings shook his head. "I don't know," he replied. "We'll go up again directly." He ordered the submarine to proceed ahead half a mile, and then rise. This was done, and as the periscope once more took in the sight about, Lord Hastings, who gazed through it, stepped quickly aside and motioned to Jack to peer in. The lad did so, and stepped back with an exclamation of delight. Frank also peered into the periscope, and uttered an exclamation of pleasure as his eyes took in the scene about. Speeding forward in the wake of the German cruisers, which the periscope made plain, were all the German torpedo boats, except three. These lay helpless upon the surface of the sea, and it was plainly evident that they were settling rapidly. Their crews were hurriedly getting out the small boats, and jumping overboard. The D-16 had done her work well. Frank turned away from the periscope. "Three notches in the table," he said to Jack, who stood at his side. "Right," replied the latter briefly. Feeling perfectly secure now, Lord Hastings ordered that the submarine be brought to the surface, and followed by Frank and Jack, he stepped out on the bridge. They stepped out just in time to see the sinking of the _Bluecher_ by the British cruiser _Lion_, and from their posts they watched the chase of the others. Frank and Jack were greatly surprised when the British admiral signalled for his ships to draw off. "Great Scott!" exclaimed Frank. "He had them right in his hands. Why didn't he follow 'em up?" "It's too deep for me," said Jack, in some disgust. "Come, come," said Lord Hastings. "You must give the Admiral credit for having some sense, you know." "Then why did he do it?" questioned Frank. "Why," said Lord Hastings, "because, had he followed another mile, the entire British fleet might have been sent to the bottom." "What do you mean?" asked Jack. "Mines," replied Lord Hastings. "The enemy has reached the protection of his mine field." "I see," said Frank, somewhat taken aback. "Of course. I should have known that the Admiral had some good reason for not following up his advantage." "You let your feelings get away with you sometimes," said Lord Hastings. "Well, I'll promise not to do so any more," said Frank. "I wouldn't make any rash promises, if I were you," said Jack, with a smile. "Well, I mean it," said Frank. "Oh, well, if you mean it, all right. Only you are liable to forget yourself if you are not careful." Jack turned to Lord Hastings. "Which way now, sir?" he asked.