Australian naval clearance divers had been operating under various titles since the Second World War. The Clearance Diving Branch of the navy was formally established in 1951. In 1966 during a tour of South-East Asia, a team of Australian clearance divers spent a week on an unscheduled operational attachment to a United States Navy Explosive Ordnance Disposal team based near Saigon. Brief and unofficial though their sojourn was, they became the first Australian clearance divers to serve in Vietnam.
The task that faced the eight Australian Naval Clearance Diving teams in Vietnam was complex and dangerous. The country's long coast and many rivers, and the large Mekong Delta near Saigon gave the North Vietnamese and the Viet Cong many opportunities to attack and disrupt shipping with mines and underwater obstacles, often planted by sappers known as swimmers. The attempts to combat these threats to shipping were collectively labelled 'Stable Door' operations and these were the primary task of the Australian clearance divers.
Large merchant ships, often carrying military supplies, were a particularly valuable target as were military vessels, especially those that operated in Vietnam's rivers. The Viet Cong and North Vietnamese used a range of mine types against shipping including moored and floating mines as well as those placed on the bottom of a watercourse. In the north of the country Soviet-manufactured limpet mines were employed. The mines were also transported and placed in a variety of ways. In some instances they were tethered beneath a sampan by cables that could be cut if the vessel was approached. The most common method, however, was to have the mines placed by swimmers who had been trained in North Vietnam and who then came south to carry out anti-shipping operations.
In addition to combating attacks on shipping, Australian Naval Clearance Divers were engaged in disposing of ordnance that had become unsafe, and in salvage operations. These included diving around downed aircraft to remove classified material and render any explosive material safe. After mid-1968 the Australians were also involved in operations with the South Vietnamese armed forces during which they cleared barriers along the approaches to suspected enemy positions.
All eight clearance diving contingents performed difficult, dangerous tasks, often in very unpleasant conditions. The waters in which they generally operated carried swift currents, were murky – reducing visibility considerably – and choppy. The materials with which the divers worked were unstable and, if handled incorrectly, lethal. Their work did not have the same profile as that carried out by Australian naval vessels or aviators, but it was vital to the safety of shipping, both military and civilian, in South Vietnam.