As he was talking the boat was being “trimmed” by admitting water as ballast into the proper tanks.

“The Z99,” he went on, “is a submersible, not a diving, submarine.  That is to say, the rudder guides it and changes the angle of the boat.  But the hydroplanes pull it up and down, two pairs of them set fore and aft of the centre of gravity.  They lift or lower the boat bodily on an even keel, not by plunging and diving.  I will now set the hydroplanes at ten degrees down and the horizontal rudder two degrees up, and the boat will submerge to a depth of thirty feet and run constant at that depth.”

He had shut off the gasoline motor and started the storage-battery electric motor, which was used when running submerged.  The great motors gave out a strange, humming sound.  The crew conversed in low, constrained tones.  There was a slightly perceptible jar, and the boat seemed to quiver just a bit from stem to stern.  In front of Shirley was a gauge which showed the depth of submergence and a spirit-level which showed any inclination.

“Submerged,” he remarked, “is like running on the surface under dense-fog conditions.”

I did not agree with those who have said there is no difference running submerged or on the surface.  Under way on the surface was one thing.  But when we dived it was most unpleasant.  I had been reassured at the start when I heard that there were ten compressed-air tanks under a pressure of two thousand pounds to the square inch.  But only once before had I breathed compressed air and that was when one of our cases once took us down into the tunnels below the rivers of New York.  It was not a new sensation, but at fifty feet depth I felt a little tingling all over my body, a pounding of the ear-drums, and just a trace of nausea.

Kennedy smiled as I moved about.  “Never mind, Walter,” he said.  “I know how you feel on a first trip.  One minute you are choking from lack of oxygen, then in another part of the boat you are exhilarated by too much of it.  Still,” he winked, “don’t forget that it is regulated.”

“Well,” I returned, “all I can say is that if war is hell, a submarine is war.”

I had, however, been much interested in the things about me.  Forward, the torpedo-discharge tubes and other apparatus about the little doors in the vessel’s nose made it look somewhat like the shield used in boring a tunnel under compressed air.

“Ordinary torpedo-boats use the regular automobile torpedo,” remarked Captain Shirley, coming ubiquitously up behind me.  “I improve on that.  I can discharge the telautomobile torpedo, and guide it either from the boat, as we are now, or from the land station where we were last night, at will.”

There was something more than pride in his manner.  He was deadly in earnest about his invention.