“You see what you have to do, Kline,” said Major Woodruff, presently.  Then the older officer turned to Jack to say: 

“Mr. Benson, since Mr. Farnum has been kind enough to place you and the boat at our orders, Kline is going to remain on board, today, during the tests.  He will give Mr. Somers whatever orders are necessary in order to make the tests most successful.”

“Why not give the orders to me, sir?” Jack asked.

“Why, you see, Mr. Benson,” replied the major, “I plan for you to be on shore, out on the neck, to make certain observations regarding the work of your craft.  Those observations you will turn in to me.”

“Very good, sir.  The neck, I take it, is the narrow strip of land that separates this part of the bay from the ocean?”

“Quite right, Mr. Benson.”

It was to be observed that the major, like naval officers, addressed Jack by the title of “mister,” not “captain.”  This was because, in the military service, Army and Navy titles are not recognized unless conferred by government appointment or commission.  Hence, though young Benson was “captain” to his crew and to civilians, officers of the United Service could address, him only as “mister.”

“The neck, Mr. Benson,” continued Major Woodruff, “is the land best suited for watching our work from to-day.  And now, I will state what the object of to-day’s tests is.  This morning our tug will be engaged in planting certain submarine mines.  Mr. Somers will watch our work of planting.  Of course the mines will contain no explosives.  You young men have, I understand, solved the problem of leaving a submarine boat while it lies on the bottom?  You are also able to enter the submarine again from the surface?”

“Quite right, Major,” Jack nodded.

“Then, if Mr. Somers watches the planting of the dummy mines, he will have the same advantage as would the commander of an enemy’s submarine in knowing where our mines are planted.  We shall plant four of them, this morning, and Mr. Somers, after seeing each mine planted, will mark down its position on a chart of the bay.  He will then take the boat outside, enter under water, and, without touching any of our mines, while handling the boat, will see if he can stop close by and cut the connecting wires.”

“If your mines contain no explosive, Major,” Eph inquired, “how are you going to be able to tell whether I collide gently with one of your submarine mines?”

“We shall know at once,” smiled Major Woodruff.  “If you should collide with one, you will cause, a bell to be rung in the camera obscura room over at the fort.  The bell that rings will show us which one of the mines you touched against.”