A Diver Propulsion Vehicle or a DPV is an item of diving equipment used by scuba divers to increase their range while underwater where their endurance is restricted due to limited availability of breathing gas and need to avoid decompression sickness. A DPV generally consists of a battery-powered electric motor which drives a propeller. The machine should be designed to avoid some predictable operating problems. It should be neutrally buoyant in the water. The diver should not be able to accidentally start the motor. The propeller should be shielded so that it does not damage the diver, the diver`s equipment or marine life. DPVs are useful for long journeys at constant depth where navigation is easy. Some divers engaged in cave diving and technical diving use DPVs. The machine helps move the bulky equipment the divers carry. It also allows them to make better use of their short underwater time because they have greater decompression requirements due to deep diving. For many recreational divers DPVs are not useful. Buoyancy control is vital for diver safety: the DPV has the potential to make buoyancy control difficult and cause barotrauma if the diver ascends or descents under power. Navigation in visibility of less than 5 metres using a DPV could be difficult. Also, many forms of smaller marine life are very well camouflaged or hide well and are only seen by divers who move very slowly and are very vigilant.