He bowed, and left them.

"I don't know as I am particularly fond of this kind of travel,"
Frank confided to Jack. "It's all right as long as we remain on
the surface, but I'll bet it would feel queer to be moving along
under the water."

"Right you are," replied Jack. "However, we are here and we
shall have to make the best of a bad situation. Then, too,
perhaps we can learn something that may prove of use to us later
on."

The lads dined that night at the officers' mess and became quite
well acquainted with all of them. They found Captain von Cromp
not half so gruff as he had been when they first came aboard.
They were questioned about the service they had seen, and their
story greatly surprised all the officers.

Upon Lieutenant Stein's request, the commander granted the lads
permission to look over the vessel.

The lieutenant showed them how the vessel was submerged, by
allowing one of the tanks to fill with water; how it rose again
by forcing the water from the compartment by means of compressed
air; how the air was purified when a lengthy submersion was
necessary, and how the vessel was handled in times of action.

He showed them the periscope, and allowed them to peer through,
although there was no need to use this, as the vessel was above
water.