Tom closed the water-tight door of the conning tower. Word was sent through the tube to the engine-room that a more severe test of the ship was about to be made. The craft was now outside the line of breakers and in the open sea.
"Is everything ready, Tom?" asked his father in a quiet voice.
"Everything," replied the lad nervously, for the anticipation of being about to sink below the surface was telling on them all, even on the calm, old sea captain.
"Then open the tanks and admit the water," ordered Mr. Swift.
His son turned a valve and adjusted some levers. There was a hissing sound, and the Advance began sinking. She was about to dive beneath the surface of the ocean, and those aboard her were destined to go through a terrible experience before she rose again.
Chapter Eleven
On the Ocean Bed
Lower and lower sank the submarine. There was a swirling and foaming of the water as she went down, caused by the air bubbles which the craft carried with her in her descent. Only the top of the conning tower was out of water now, the ocean having closed over the deck and the rounded back of the boat. Had any one been watching they would have imagined that an accident was taking place.
In the pilot house, with its thick glass windows, Tom, his father and Captain Weston looked over the surface of the ocean, which every minute was coming nearer and nearer to them.