Successful sea trials of RUFAS II (a towed, unmanned data-gathering submersible capable of operating to a depth of 2,400 feet) were conducted in the Gulf of Mexico. This paper describes the vehicle automatic flight control system, which is designed to follow the terrain of the ocean floor at a constant height above bottom and to maintain a level zero roll flight condition even against strong cross currents. Results showed that an inexpensive digital depth sounder type of sonar is entirely adequate for height above bottom information and that location of the transducer can provide positive or negative feedback. The stabilizing feedbacks used to damp the system are (1) vane position and (2) output rate feedback, which are remotely controlled (from the tow vessel) depending on the time response desired. A preset minimum height above bottom is. designed into the control system to prevent the vehicle from accidently crashing into the sea bottom.