"There is of course," the lieutenant went on, "a crudely defensive measure called the torpedo net. These are meshes of strong steel which are dropped down from the side of the warship and are supposed to catch the torpedo before it hits the side of the ship."
"Well, don't they?" asked Frank.
"In theory," said the lieutenant, "the torpedo explodes within the net and the force of its attack is more or less diminished. As a matter of fact, however, torpedo nets are not dependable. Why, most of our submarines are equipped with a formidable device for cutting these nets. This device, in one form, resembles an enormous pair of sheers which cut through the nets like paper. In another form they are equipped with powerful tearing arms which drag the net away and expose the sides of the battleship to the deadly messenger from the torpedo tube. Am I tiring you?"
"I should say not," replied both lads in one breath, and Frank added: "I don't just understand how a submarine sinks and rises."
"It's very simple," said the lieutenant, "and at the same time I'll tell you something else. The submarine is unaffected by tempests, and for this reason also is more deadly than a battleship. The submarine can dive down into the depths where there is no movement of the waves, and it can remain under water for fourteen hours continuously. This is accomplished by tanks which can be filled with water and, overcoming what is known as the 'margin of buoyancy,' submerge the vessel. The air is replenished by special purifying devices and by tanks of oxygen. When the vessel wants to rise, it simply pumps out the water from the tanks."
"It certainly is a wonderful invention," said Frank, when the lieutenant had concluded his explanation.
"Indeed it is," agreed Jack.
"You should be aboard when we are in action," smiled the lieutenant. "I am sure you would be greatly interested."
"I don't doubt it," said Jack, "although from what you have told us regarding the deadliness of submarines, I believe that I should rather witness action on a British submarine."
"Nevertheless," said the lieutenant, "you are likely to see action aboard the X-9, for I do not believe Captain Von Cromp will return to port until he has at least tried the effect of his torpedoes, on a ship or so of your countrymen."