"Be ready, Sergeant," calls the officer, warningly, to a non-commissioned
officer who stands before a board on the wall on which are several
electric push-buttons, each numbered.

"Yes, sir," replies the sergeant.

At this moment the officer sees the image of the battleship passing
fairly over the dot on the white map that is numbered nineteen.

"Fire nineteen, Sergeant," calls the Army officer in charge.

The non-commissioned officer quickly presses electric button numbered
nineteen. As he does so the electric current is sent flashing, perhaps
along four or five miles of insulated wire on the bottom of the harbor.
At the other end of that wire is submarine mine number nineteen. In a
breathless instant the current traverses the whole length of the wire.
The spark has reached the gun-cotton! There is a dull, booming sound;
a great column of water shoots up from the surface. In the midst of the
commotion the enemy's battleship is rent, and all on board, perhaps
killed. The cool, dry-eyed Army officer bending over the white
screen-map sees all this scene of horror depicted under the white
surface beneath his eyes. He knows that submarine mine number nineteen,
planted out there in the harbor, has done its duty in protecting this
portion of the coast of the United States.

Here, at Fort Craven, it was desired to find whether an enemy's submarine
boat could creep in, below the surface, find the mine, whose location
was already known through spies, and effectively cut the firing wire.
If this could be done, then, in war-time, it might be that the sergeant