Clearance diver A clearance diver was originally a specialist naval diver who used explosive s underwater to remove obstructions to make harbours and shipping channels safe to navigate , but later the term " clearance diver " was used to include other naval underwater work . Units of clearance divers were first formed during and after the Second World War to clear ports and harbours in the Mediterranean and Northern Europe of unexploded ordnance and shipwrecks and booby trap s laid by the Germans . Within the Royal Navy there are two distinct types of professional military diver and although the selection process for both is similar the overall training is more extensive for the RN Clearance Diver . The major distinction between the two is the level and depth of training and consequently the role of each . The qualification of Ship ' s Diver is usually a sub - qualification obtained in addition to the seaman ' s main trade , whereas the RN Clearance Diver is a full time diving specialist ( Maj R Cameron - Wilton ) In some navies , including Britain ' s Royal Navy ( RN ) , work divers , which includes Ship ' s divers must have a line and a linesman when possible . History . The first units were Royal Navy Mine and Bomb Disposal Units . They were succeeded by the " Port Clearance Parties " ( P Parties ) . The first operations by P Parties included clearing away the debris of unexploded ammunition left during the Normandy Invasion . Six groups of Clearance Divers including Commonwealth and European allied forces were in operation by 1945 . Naval work diver training is much longer and harder than sport diver training and has much stricter entry requirements . For a long time navies used the old - type heavy standard diving dress when work needed doing underwater . During and after World War II some of them started using frogman - type gear when frogman ' s kit became available . Later they started often using open - circuit scuba gear for work diving . Nations with naval work diving groups . Australia . The Royal Australian Navy ' s Clearance Diving Team s ( CDTs ) also serve as combat divers . United Kingdom . British Royal Navy naval work divers are officially called Clearance Divers . During WWII they at first often used the Davis Submerged Escape Apparatus and no diving suit , and no swimfins and they swam by breaststroke . On 1942 December 17 ( ref . Decima Flottiglia MAS # 1942 ) , 6 Italians on three manned torpedo es attacked Gibraltar harbor . A British patrol boat killed one torpedo ' s crew ( Lt . Visintini and Petty Officer Magro ) with a depth charge . Their bodies were recovered , and their swimfin s were taken and used by two of Gibraltar ' s British guard divers ( who dived with Davis Escape Set s and ( up to here ) breaststroke swimming and no fins ) ( Sydney Knowles and Commander Lionel Crabb ) . This was the first known British frogman use of swimfin s , rather than a Sladen suit and weighted boots riding a Chariot . In 1944 November in Livorno in Italy an Italian frogman called Vago came over and joined the British frogman team and brought them two Decima Flottiglia MAS issue oxygen rebreather s , which proved better in use than Davis Submerged Escape Apparatus es and lasting longer on a dive . He also brought them an Italian light 2 - piece frogman ' s drysuit : before then they dived with their skin exposed . For many years Clearance Divers used the Siebe Gorman CDBA rebreather . In 1982 Clearance Divers were heavily involved in the Falklands War , in which Britain recaptured the Falkland Islands from Argentina . They received many awards and medals for their work on mines and disposing of 1000 - pound bombs lodged in British warships . In the 1990s they used a type of automatic mixture rebreather which is so heavy that on surfacing after a dive even a very physically fit naval diver preferred to remove the rebreather while still in the water and have it craned out separately . Other combinations of kit used in the past by British Clearance Divers ( work divers ) were :