"I'll show you," replied Frank grimly. "Give me the gun!"
Without another word Jack passed the weapon to his friend.
"Now," said Frank, "lower yourself over the side of the boat and when I say dive, dive!"
"See here," said Jack, taking Frank by the arm. "Have you gone crazy? What do you think you are going to do?"
"I don't think anything about it," replied Frank, more quietly now. "I know what I am going to do."
"Well, what is it then? Out with it."
"Do you see that object hanging to the periscope tube on the submarine?" asked Frank.
"Yes, I see it. Why?"
"Don't you know what it is?"
"No; what is it?"