It was now a running fight, and yet not so much that, because to run was impossible. However, they hurried all they could, and, by dint of quick firing kept the ugly creatures at bay until the side of the ship, where the diving tank was placed, was reached.
The professor stepped to one side, and motioned for the others to proceed him in entering. Little time was lost. As Bill, the last one in, stepped past the steel door the inventor attempted to enter. To do so he had to let go of his gun.
Instantly one of the sharks made a rush for the old man. But Andy was on the watch. He leaned forward, and, from his weapon sent a bullet straight down the throat of the monster. The electric missile did its work well, and the lifeless body of the shark was devoured by the others of its tribe.
The professor pulled the door shut behind him. Then he set the pump to work to empty the tank. As he did so there was a tremor to the ship. What could it mean?
In a few minutes the tank was empty and the divers stepped out into the ship, freed from the oppressive weight of water. The ship continued to vibrate and seemed to be in motion.
"What is it?" asked Mark as soon as he had his helmet off.
"De ship am free! We've got off de mud bank!" exclaimed Washington, running in from the engine room.
It was true. Enough had been dug so that, with the power of the screw working backward, there was sufficient force to pull the Porpoise from her perilous position.
"Empty the tanks and rise to the surface," said the professor.
In a few minutes the ship was on top of the waves, the adventurers freed from the double danger of the mud and sharks. They congratulated each other on the good outcome of the fight with the monster fishes.