These machines have largely taken over from manned submersibles and submarines, due to their versatility, dependability, and economy in operation. In the North Sea oil industry, these machines can stay down surveying piplines or structures, monitoring events, acting as "eyeballs" for saturation divers, or carrying out other tasks for days at a time. When a "crew-change" is necessary, the operators simply stand up and walk away from a control panel and a new shift takes over.

The vehicles themselves can be extremely large, weighing many tens of tonnes, or extremely rudimentary, little more than a waterproof tv camera with a light bulb attached. I mention the latter extreme case because passengers on the Loch Ness Cruises boat "Nessie Hunter" will have seen the unit I developed over the summer of '99, which was exactly as described. The illumination came from a 5 watt lamp removed from my Austin Metro. It was simply soldered to the ends of two wires supplied with 12 volts from the surface. The ends were not insulated, and the bulb was not protected in any way. It cost 20 pence and functioned down to 40 metres.

Most ROVs are much more complex than that, of course, and they are equipped with various thrusters, sonars, compasses and manipulators to give them the ability to find their way around, avoid obstacles, and perform useful physical tasks. One such machine is the Sutech Sea Owl in the photograph below. It was brought to Loch Ness in the early 1990's and was very successful in locating and recovering underwater targets discovered earlier with sonar from the surface.