“Do you think you can head due east, and keep to that course under water, Mr. Surles?” asked the young submarine instructor.

“Yes, sir.”

“Take the wheel, then.  I will send two more men up here to observe with you.”

Stepping down to the cabin floor, Jack chose two more midshipmen, ordering them up into the tower.

“The rest of you will crowd about me, as I handle the submerging machinery,” called Jack, raising his voice somewhat.  “Ask any questions you wish, at appropriate times.”

“I thought, sir,” spoke up one of the middies, “that you controlled the diving apparatus from the conning tower.”

“It can be done there, when the officer in charge of the boat is up there,” Jack answered.  “The diving, and the rising, may be controlled at this point in the cabin.  Mr. Hastings, give us eight miles ahead from the electric motors.”

“Yes, sir,” came the word from Hal.

“Pass the word to Mr. Surles to keep to the course,” added Benson.

Under the impetus from the electric motors, which were used when going under water, the propeller shafts began to throb.

“We’re going down, now, gentlemen,” called Jack.  “Observe the shifting record on the depth gauge, as we go lower and lower.  Also, look out for your footing, for we dive on an inclined plane.  Now—­here we go!”

The next instant they shot below, going down at so deep an angle that it made many of the middies reach for new footing.

“The gauge registers sixty feet below,” announced Jack Benson, in a tone to be heard above the murmurs of some of the young men.  “Now—!”

In another moment, by the quick flooding of some of the compartments astern, the young skipper brought the boat on an even keel.

“Someone ask the men up in the tower how far they can see through the water,” proposed Jack.

“Can’t see a blessed thing,” came down the answer.  “Except for the binnacle light over the compass we might think ourselves at the bottom of a sea of ink.”

“That’s one of the peculiarities of submarine boating,” explained Jack Benson.  “A good many land-lubbers imagine we use powerful searchlights to find our way under water, but a light powerful enough to show us twenty feet ahead of our own bow hasn’t yet been made by man.  So, when you dive beneath the surface, you simply have to go it blind.  As a result, you take your bearings and guess your distance before you dive.  That guess is all you have to go upon in judging where to come up to strike at an enemy’s hull.  But that guess can be made with splendid accuracy when you understand your work well enough.”

After having finished the prescribed distance under water, Captain Jack turned on the compressed air to expel the water gradually from the compartments.  So easily was this done that there was no real sensation of rising.  Suddenly the conning tower appeared above water.  There was a quick rush upward for the platform deck.  None of these middies ever having been below before, in a submarine boat, several of them had been on tenterhooks of anxiety.  Not one of them, however, by word or gesture had betrayed the fact.