A remote operated vehicle system comprises a topside, a fish equipped with a GPS receiver, a transmitter for transmitting GPS position data, and a receiver operable to receive the transmitted position data. Transmission may be from the fish to the topside or from the topside to the fish. Alternatively, a second transmitter and receiver give two-way transmission. These arrangements allow the position of the fish to be monitored or tracked, so that it can be readily rescued in the event of damage or breakdown. Alternatively, predetermined position data can be sent to the fish, allowing it to automatically navigate a desired route. Particular embodiments include an umbilical cable for connecting the fish and the topside together and operable to carry signals, including position data, between the two, an additional GPS receiver on the topside so that the fish can navigate to the topside unaided, and a buoyancy control device which brings the fish to the surface.