"Simple enough, apparently. The army folks are protecting the mouth of the harbor. There are important fortifications there, because in time of war the protecting fleet, or part of it, might gather there.
"The army folks have planted mines there. While watching for the Blue fleet to arrive, we are to test those mines."
"Phew!" gasped Herc. "There's only one way to test how much kick there is to a mine."
"And what's that?" asked Ned.
"To blow it up and—yourself with it," declared Herc sententiously. "Well, for a nice little holiday job, we have sure picked a dandy."
"Hold on a minute, will you?" interrupted Ned. "Let me finish this. The mines are wired up by a new system. What we have to find out is if we can sneak into the harbor mouth in our submarines and disconnect the firing wires of the mines without blowing ourselves up. If we can do this, the system is a failure."
"Humph! and so are we."
"So are we what?"
"Failures! If one of these mines blew up, what else would we be——"