"Of course," said Frank, "we, in this submarine, will have a better chance of performing such a raid successfully than any other vessel, because we can go beneath the water, and stay there until we get ready to come up." "Right you are," agreed Jack. "All we have to do is to figure the distance from here to a point where, being sure it is not mined, we wish to rise. Then, calculating our speed, we shall know just when to come up safely." "Perfectly simple," said Lord Hastings with a smile, "if we don't hit a mine before we get there." "Don't you think, sir, that by going beneath the mines we will be successful?" "If I didn't I wouldn't make the attempt," said Lord Hastings dryly. "I remember how you did it when you sank that Turkish cruiser in the Dardanelles." "And had we had this vessel at our disposal," said Jack, "we could have done considerable more damage. As it was we had to get back before we exhausted our air supply." "We have an advantage in that respect. There can be no question about that," said Lord Hastings. "Well, when shall we start, sir?" asked Frank. "Immediately," was the reply. The three turned their eyes over the sea to where the British fleet, retiring, could be seen moving toward the west. One of the large cruisers, the _Tiger_, was being towed by a torpedo boat. "Hope she is not badly damaged," said Jack, noticing how the British cruiser staggered. "She looks fit enough," said Frank. "The trouble is you can never tell by the looks," said Lord Hastings. "However, I guess she is in no danger of sinking." "Let us hope her death list is small," said Jack fervently. "Let us hope so," agreed Lord Hastings. "Come, we may as well go below." The commander of the D-16 descended from the bridge and the lads followed him. "We may as well submerge here," said Lord Hastings, "for every foot we advance on the surface of the water is putting us in the way of hitting a German mine. We can't be too careful." "But it is hardly likely there would be any about here, sir," said Frank. "Have you forgotten what it was that caused Admiral Beatty to give up the pursuit of the enemy?" asked Lord Hastings. "That's so, sir," said Frank. "I had forgotten." "Besides," said Jack, "the Germans may have dropped more mines to cover their retreat." "Exactly," said Lord Hastings. "Well, let's dive then," said Frank. "The sooner the better it will suit me," said Jack. "So be it then," from Lord Hastings. "You may give the order, Mr. Templeton." Jack obeyed, and slowly, as the water was let into her tanks, the D-16 sank and sank, until, certain that she was beneath the enemy's mines, Lord Hastings gave the command: "Full speed ahead!" CHAPTER V. TROUBLE ON BOARD. "It's as well to go quickly," Lord Hastings said, giving his reason for ordering full speed ahead. "I hardly anticipate they have mined very deep here. We'll slow down further along."