vessel
could readily navigate over the waterbed itself, and that while
navigating on the waterbed a door could be opened in the bottom
of a compartment and the water kept from entering the vessel by
means of compressed air, and that the crew could, by donning
diving suits, readily leave and enter the vessel while submerged.
Another novel feature was in the method of controlling the depth
of submergence when navigating between the surface and waterbed.
The vessel was designed to always submerge and navigate on a
level keel rather than to be inclined down or up by the back, to
"dive" or "rise." This maintenance of a level keel while
submerged was provided for by the installation of four depth
regulating vanes which I later termed "hydroplanes" to
distinguish them from the forward and aft levelling vanes or
horizontal rudders. These hydroplanes were located at equal
distances forward and aft of the center of gravity and buoyancy
of the vessel when in the submerged condition, so as not to
disturb the vessel when the planes were inclined down or up to
cause the vessel to submerge or rise when under way.

I also used, in conjunction with the hydroplanes, horizontal
rudders which I then called "levelling vanes," as their purpose
was just the opposite from that of the horizontal rudder used in
the diving type of vessel. They were operated by a pendulum
controlling device to be inclined so as to always maintain the
vessel on a level keel rather than to cause her to depart
therefrom. When I came to try this combination out in practice, I
found hand control of the horizontal rudders was sufficient. If
vessels with this system of control have a sufficient amount of
stability, you will run for hours and automatically maintain both
a constant depth and a level keel, without the depth control man
touching either the hydroplane or horizontal rudder control gear.
This automatic maintenance of depth without manipulating the
hydroplanes or rudders was a performance not anticipated, nor
claimed in my original patent on the above-mentioned
combination, and what caused these vessels to function in this
manner remained a mystery, which was unsolved until I built a
model tank in 1905 in Berlin, Germany, and conducted a series of
experiments on models of submar