I submitted designs of a twin-screw vessel eighty feet long, ten feet beam, and one hundred fifteen tons displacement, with 400-horsepower steam engines for surface propulsion and 70-horsepower motors for submerged work. This design introduced several new and striking features into the art of submarine navigation which have been the cause of considerable scientific discussion. The design called for a _double hull_ vessel, the spaces between the inner and outer hulls forming water-ballast tanks; the design also called for twin screws and four torpedo tubes, two firing forward and two aft. [Illustration: LAKE DESIGN AS SUBMITTED TO THE U. S. NAVY DEPARTMENT IN 1893 Novel features consisted in: (A) wheels for running on the bottom; (B) rudder forming also a steering wheel when navigating on the bottom; (C-C) propellers for holding vessel to depth when not under way; (D-D) depth regulating vanes or hydroplanes for causing vessel to change depth while under way and to accomplish the changes of depth on an even keel; (E-E) horizontal rudders or "leveling vanes" designed to automatically hold the vessel on a level keel when under way; (F) a weight automatically controlled by a pendulum; (P) mechanism to correct trim; (G) gun arranged in watertight revolving turret for defense purposes or attack on unarmored surface craft; (L) propeller in tube for swinging vessel at rest to facilitate "pointing" her torpedoes; (M) conning tower; (N) telescoping smokestack; (O) observing instrument arranged to turn down on deck when under way; (T-T) torpedo tubes, two firing forward and two aft; (W-W) anchoring weights to hold the vessel at rest at any desired depth between the surface and bottom; (X) an "emergency keel" which would be automatically released if the vessel reached an unsafe depth. She was a double-hull vessel, water being admitted to the space between the inner and outer hulls and in trim tanks forward and aft to effect submergence. A diving compartment was also provided to enable the crew to leave or enter the vessel while submerged.]