Tom called for some of his men to take charge of the steering and running of the Mars while he and Lieutenant Marbury prepared to fire the two larger weapons. This was to be one of the most important tests.
Service charges had been put in, though, of course, no projectiles would be used, since they were then flying over a large city not far from Shopton.
"We'll have to wait until we get out over the ocean to give a complete test, with a bursting shell," Tom said.
He and Lieutenant Marbury were beside a gun, and were about to fire it, when suddenly, from the stern of the ship, came a ripping, tearing sound, and, at the same time, confused shouts came from the crew's quarters.
"What is it?" cried Tom.
"One of the propellers!" was the answer. "It's split, and has torn a big hole in the gas bag!"
"Bless my overshoes!" cried Mr. Damon. "We're going down!"
All on board the Mars became aware of a sudden sinking sensation.