As Tom Smith and Bill Jones were hungry a hasty meal was prepared for them, during the eating of which they told of their experiences since landing from the airship. They had been on a farm until fired with a desire to go roving once more. For the next few days the professor, the boys, and the other four were busy making some improvements to the _Porpoise_. Tom and Bill were much astonished at their first sight of the queer craft, but they soon became accustomed to her, and said they preferred her to the airship. "To-morrow we are going on a little longer trip than our first trial," announced the inventor one evening. "We will be gone all day if nothing happens to make the stay more lengthy," he added grimly. "So, Washington, put plenty to eat aboard." A little later, when supplies had been put on the _Porpoise_, and the machinery well overhauled, the professor explained that he intended making a trip, entirely under water, from the dock in the cove to a point off the Massachusetts coast and return. Early the next morning all were aboard. To each one was assigned a particular station. Washington, with Mark as an assistant, was in the engine-room. Jack was to watch the various gages and registers to give warning of any danger. The professor, of course, would be in the conning tower and operate the craft. Andy was to be with him, to watch out, with his sharp eyes, for any danger that might loom up in the path of the searchlight. Tom and Bill were to be ready to help where needed. With a hissing sound the water filled the tanks and the _Porpoise_ sunk beneath the waves. The engine that worked the endless screw was started, and the threads, working on the water cable, shot the boat ahead. "We're off!" yelled Washington. About sixty feet below the surface the craft was sent along. Mile after mile was covered as shown by the patent log. The lights were turned off, and through the thick plate glass windows the strange inhabitants of the sea were observed. "I think I'll go a little nearer the surface," said the professor to Andy. The inventor started the pumps that emptied the tanks. The craft rose slightly. "Quick! Stop her!" shouted the old hunter, grasping the captain's arm. Something black, like a grim shadow, loomed up in the dull glare of the searchlight. "What is it?" cried the professor. "We're goin' to hit somethin' hard!" yelled Andy. "It's the hull of a ship!" exclaimed the inventor as he jammed the reversing lever hard over. It was too late. The next instant the _Porpoise_, with a shock that made her shiver from stem to stern, collided with the steel side of a small warship. CHAPTER IV IN THE MIDST OF FIRE "Pull the secondary emergency lever!" cried the professor through the speaking tube to Washington. "We must reach the surface at once!" "Are we damaged?" asked Andy, scrambling to his feet, for the shock had knocked him down. The professor had not fallen because he clung to the steering wheel.