"Put it down, quick! Do you want to blow us all up?"
"What do you suppose it's doing here?" asked Frank, still holding the object out at arm's length.
"How should I know? But I suppose all submarines carry them. I have heard that many have been planted by submarines."
For the object that Frank held in his hand was a small melinite floating mine!
"I suppose this would blow any ship to kingdom come, wouldn't it?" asked the lad.
"I should say it would; so you had better put it down unless you want to send us all there."
Frank leaned close to his chum, and whispered rapidly:
"See if you can't find a gun around before the lieutenant comes back. Quick! A revolver, rifle, or anything!"
"What for?" demanded Jack, in surprise.
"Never mind what, for. Look quick, while I hide this thing under my coat."