Diver propulsion vehicle A diver propulsion vehicle ( DPV , also known as an underwater propulsion vehicle or underwater scooter ) is an item of diving equipment used by scuba and rebreather divers to increase range underwater . Range is restricted by the amount of breathing gas that can be carried , the rate at which that breathing gas is consumed under exertion , and the time limits imposed by the dive tables to avoid decompression sickness . DPVs can have military application . Structure . A DPV usually consists of a pressure resistant watertight casing containing a battery - powered electric motor , which drives a propeller . The design must ensure that the propeller cannot harm the diver , diving equipment or marine life , the vehicle cannot be accidentally started or run away from the diver , and it remains neutrally buoyant while in use underwater . Application . DPVs are useful for long journeys at constant depth where navigation is easy . Typical uses include cave diving and technical diving where the vehicles help move bulky equipment and make better use of the limited underwater time imposed by the decompression requirements of deep diving . Military applications include delivery of combat divers and their equipment over distances or at speeds that would be otherwise impracticable . Disadvantages . 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 descends under power . Visibility of less than 5 metres makes navigating a DPV difficult . Also , many forms of smaller marine life are very well camouflage d or hide well and are only seen by divers who move very slowly and are very vigilant . Types . Diver - tugs , tow - behind , scooters . The most common type of DPV tows the diver who holds onto handles on the stern or bow . Tow - behind scooters are most efficient by placing the diver parallel to and above the propeller wash . The diver wears a harness that includes a crotch - strap with a D - ring on the front of the strap . The scooter is rigged with a tow leash that clips to the scooter with releasable metal snap . Manned torpedoes . These are torpedo or fish - shaped vehicles for one or more divers typically sitting astride them or in hollows inside . The well known human torpedo or " chariot " was used by commando frogmen in World War II . Similar vehicles have been made for work divers or sport divers but better streamlined as these do not have warheads ; the " Dolphin " made on the Isle of Wight ( UK ) in the 1970s is an example . Some Farallon and Aquazepp scooters are torpedo - shaped with handles near the bow and a raised seat at the rear to support the diver ' s crotch against the slipstream . The Russian Protei - 5 and Proton carry the diver attached to the top . The New Zealand made Proteus is strapped onto the diver ' s cylinder . Subskimmers . The Subskimmer is a submersible rigid - hulled inflatable boat ( RIB ) . On the surface it is powered by a petrol engine , when submerged the petrol engine is sealed and it runs on battery - electric thrusters mounted on a steerable cross - arm . It can self inflate and deflate , transformimg itself from a fast , light , surface boat to a submerged DPV . Started in the 1970s by Submarine Products Ltd . of Hexham , Northumberland , England , " Subskimmer " is now a tradename owned by Marine Specialised Technology . Wet subs . As DPVs get bigger they gradually merge into submarine s . A wet sub is a small submarine where the pilot ' s seat is flooded and the diver must wear diving gear . Covert military operations use swimmer delivery vehicles ( SDVs ) to deliver and retrieve operators into harbors and near - shore undetected . An example is the Multi - Role Combatant Craft ( MRCC ) . Manta - boards . These are unpowered boards ( usually rectangular ) towed by a surface boat with two ropes . The diver holds onto it and keeps it submerged by adjusting the angle like an upside - down aerofoil . It is named after the manta ray fish . Modern DPVs . Here is a list of some of modern DPVs currently in service . China . All confirmed DPVs in Chinese service are developed by the Kunming Wuwei Science & Technology Trade Co . , Ltd at Kunming , a solely owned subsidiary of Kunming 705th ( Research ) Institute Science & Technology Development Co . ( 昆明七零五所科技发展总公司 ) ] at Kunming , which in turn , is a company wholly owned by the 705th Research Institute ( headquartered in Xi ' an ) of the China Shipbuilding Industry Corporation . All DPV / SDVs ( swimmer transportation devices ) fielded by this contractor are developed by the design team with the following members : Liu Ning ( 刘宁 ) , You Yun ( 犹云 ) , Jin Zhongxian ( 金仲贤 ) , Chen Haizhen ( 陈海珍 ) , and Zhang Chun ( 张春 ) . A total of 4 DPVs have been identified in Chinese naval service : In addition to the DPVs currently in the Chinese naval inventory , Glory International Group Ltd in Beijing is also marketing two of its DPVs , ( GL602 and GL603 ) , to the Chinese military . Sweden . Swedish firm Defence Consulting Europe Aktiebolag ( stock company , often abbreviated as DCE AB ) has developed a family of SDV of modular design , all of them based on the same basic frame and general design principle , and current available versions include : United Arab Emirates . After purchasing US submersible manufacturer Seahorse Marine , Emirate Marine Technologies of United Arab Emirates has developed four classes DPV / SDV , all of them built of glass reinforced plastic and carbon composite materials : Yugoslavia . All SDVs of former Yugoslavia were developed by BRODOSPLIT - BRODOGRADILIŠTE SPECIJALNIH OBJEKATA d . o . o . , which have been passed on to successor nations of former Yugoslavia .