his hours of rest."

"Then you have two enlisted men aboard who thoroughly understand
your engines?" pressed Dave Darrin.

"Ordinarily," replied Hal Hastings, here breaking in. "But one
of our engine-tenders reached the end of his enlisted period to-day,
and, as he wouldn't re-enlist, we had to let him go. So the new
enlisted man whom we took aboard is just starting in to learn
his duties."

"Small loss in Morton," laughed Lieutenant Jack Benson. "He was
enough of a natural genius around machinery, but he was a man
of sulky and often violent temper. Really, I am glad that Morton
took his discharge to-day. I never felt wholly safe while we
had him aboard."

"He was a bad one," Ensign Hal Hastings nodded. "Morton might
have done something to sink us, only that he couldn't do so without
throwing away his own life."

"I don't know, sir, what I'd do, if I were a commanding officer
and found that I had such a man in the crew," replied Midshipman
Darrin.

"Why, in a man's first enlistment," replied Lieutenant Jack, "the
commanding officer is empowered to give him a summary dismissal
from the service. Morton was in his second enlistment, or I surely
would have dropped him ahead of his time. I'm glad he's gone."

Ensign Eph had now finished his meal and was sitting back in his
chair. Lieutenant Jack therefore gave the rising sign.

"I want to show the midshipmen everything possible on this trip,"
said the very young commanding officer. "So we won't lie here
in the mud any more. Mr. Somers, you will return to the tower
steering wheel, and you, Mr. Hastings, will take direct charge
of the engines. I will gather the midshipmen around me here in
the cabin, and show the young gentlemen how easily we control the
rising of a submarine from the bottom."

Hal and Eph hurried to their stations. The midshipmen followed
Jack Benson over to what looked very much like a switchboard.
The young lieutenant held a wrench in his right hand.

"I will now turn on the compressed air device," announced Lieutenant
Jack. "First of all I will empty the bow chambers of water by
means of the compressed air; then the middle chambers, and, lastly,
the stern chambers. On a smaller craft than this we would operate
directly with the wrench. On a boat of the 'Dodger's' type we
must employ the wrench first, but the work must be backed up with
the performance of a small electric motor."

Captain Jack rapidly indicated the points a