The gallant commander was now steering a course for the third of the Turkish cruisers. "Guess I won't go so close this time," he remarked. "I'll fire at longer range, so we won't have so far to go among the wreckage of all three when we leave." Ten minutes, later the submarine came within the desired range, unobserved by the cruiser, which was lowering her boats to go to the help of the others. Captain Nicholson stood with his hand on the toggle of the firing valve, reading the range scale. Suddenly there was a terrific shock. Every man on board the submarine was knocked off his feet, and the submarine went rapidly to the bottom. Jack was knocked unconscious by the suddenness and force of the shock. When he opened his eyes again, Frank was bending over him. "What's the matter?" he gasped. "Shot hit us, I guess," was Frank's calm reply. The lad was right. Two small Turkish gunboats, whose presence in the harbor was not known to Captain Nicholson, had approached the scene of battle, and making out the submarine's periscope, had opened on her with the big guns. One shot had gone true, and it was this that had sent the Y-3 careening to the bottom. "Are we going to sink?" asked Jack. "We've already sunk," replied Frank. "Whether we'll get to the surface again or not I don't know." The lads heard the hiss of air through the vent in the manifold. Brown was letting water into the ballast tank to keep the submarine down. He turned as Captain Nicholson walked over to him. "They got our periscopes, I think," he said coolly. "But our torpedo went just the same!" Sure enough the tube was empty. The force of the shock had caused Captain Nicholson to launch the torpedo before he was ready, and there was no knowing whether it had been aimed true or not. The commander now took account of the casualties. One of the men had an ugly gash across his forehead from being thrown against a stanchion, another had a bleeding and probably broken nose. Brown applied first aid to the injured, while Captain Nicholson got the submarine under way again and headed for the mouth of the harbor. "I wonder if that last torpedo went home," said Frank. "Do you suppose it did, captain?" "I don't know," was the reply. "We are blind now, our periscope having been shot away, and there is no way of telling without going to the surface and exposing ourselves to gunfire." "Is there any danger of our being sunk?" asked Jack. "Danger!" he repeated. "You bet there's danger. Still, thanks to a tight hull and a true compass, we have a fighting chance." The Y-3 was now making ten knots, for, as Captain Nicholson said, "there was no use wasting time and giving the enemy time to plant a barrier." Still five hundred yards from the sandbar which must be crossed, there was a jar, a moaning, grinding sound, and the motors went instantly dead. From the battery compartment there was a rush of water into the living quarters.