"Strange," said Mr. Henderson. "I wonder if anything is wrong with the machinery." "More like the whale, or whatever it is, is on top of the boat, holding her down," suggested Andy. There was no doubt of this a moment later, for there were several violent blows on the upper part of the _Porpoise_. The crew of the submarine were held prisoners below the surface by the unknown monster! For a few minutes the thought of the awful fate that would be theirs if the ship should be wrecked under the water made each one speechless. As they stood looking at each other, not knowing what to do, the attack was renewed on the port side. The big fish, whale or whatever it was, kept pounding away. "I have an idea!" cried Andy suddenly. "What is it?" asked the professor quickly. "Let me put a diving dress on," began the old hunter. "I tell you we can't sink to the bottom in this depth of water," interrupted the professor. "We don't need to," put in Andy. "All I want is a diving suit and a chance to stand out in the diving chamber. I guess I can fix Mr. Whale, if I have one of those electric guns." "Quick! Get a diving suit, Washington!" cried Mr. Henderson. He saw what the old hunter planned to do. In a few minutes Andy was dressed in the suit. The attacks of the monster had redoubled in frequency, and the ship rocked as in a storm. Andy stepped into the diving chamber, clasping the electric gun. The inner door was tightly closed and then the sea cocks that admitted water from the outside were opened. When the pressure inside the chamber was equal to that of the ocean outside some one pulled the lever that opened the outer door. Andy knew better than to step outside. He remained in the chamber, like a sentinel hid in the embrasure of a wall, for the chamber was a sort of big dent in the side of the _Porpoise_. Once more the ship rocked from a terrific blow, and the old hunter was nearly thrown out and into the fathomless depths below. He clung to the door lever and peered out. Through the big glass eyes of his copper helmet he saw headed straight at him a whale that seemed larger than the submarine. CHAPTER XI CAUGHT IN A SEA OF GRASS "It's all up with me and the ship, too," thought Andy as he stood in the small chamber and watched the oncoming of the monster. However, he was not going to die without a fight, so he raised the electric gun. Yet he knew it was a most forlorn chance. He aimed straight down the big open mouth and pulled the trigger. The next instant the water all about him was a mass of foam, through which he could dimly see that the whale had halted. And, as the old hunter watched, in awe and fear at what he saw, he noted that instead of one monster there seemed to be a pair. Together they were threshing the sea into a bloody foam.