The Idea was that a brushless motor would act as a propeller, with that would rotate it. 2 pumps located on the outside of the submarine would be used to pump in/out water into the main body. A small water-proof case is located in the middle with the lipo and all other non-waterproof components. Waterproof cable glands were used to between inside/outside and the inside/waterproof box. Because of the inability to communicate under water, a flotation buoy was used above the surface. A NRF24L01 module was used for both the receiver and the transmitter. A Arduino acted as the brain. A lipo was used as a battery, and relays controlled the various motor. The transmitter was just a box with another Arduino, two switches for the pumps, and a joystick for the servo and motor.
Problems: The design was too buoyant and constantly leaked water. The electronics were waterproofed with an electronic waterproof coating (pretty much nail polish), and the submarine was weighed down with a bolt weight vest (still would not sink!). From all my expierence, it was clear that It was in dire need of a total redesign, but I decided to move on, since it would have been costly.
Pictured is the weight vest.