until 1974. Builders still occasionally find unexploded bombs, such as on the site of the destroyed Hippodrome Theatre in 1984. Despite efforts by the city council to build new housing, a 1955 survey indicated that 7,000 houses in Portsmouth were unfit for human habitation. A controversial decision was made to replace a section of the central city, including Landport, Somerstown and Buckland, with council housing during the 1960s and early 1970s. The success of the project and the quality of its housing are debatable. Portsmouth was affected by the decline of the British Empire in the second half of the 20th century. Shipbuilding jobs fell from 46 percent of the workforce in 1951 to 14 per cent in 1966, drastically reducing manpower in the dockyard. The city council attempted to create new work; an industrial estate was built in Fratton in 1948, and others were built at Paulsgrove and Farlington during the 1950s and 1960s. Although traditional industries such as brewing and corset manufacturing disappeared during this time, electrical engineering became a major employer. Despite the cutbacks in traditional sectors, Portsmouth remained attractive to industry. Zurich Insurance Group moved their UK headquarters to the city in 1968, and IBM relocated their European headquarters in 1979. Portsmouth's population had dropped from about 200,000 to 177,142 by the end of the 1960s. Defence Secretary John Nott decided in the early 1980s that of the four home dockyards, Portsmouth and Chatham would be closed. The city council won a concession, however, and the dockyard was downgraded instead to a naval base. On 2 April 1982, Argentine forces invaded two British territories in the South Atlantic: the Falkland Islands and South Georgia and the South Sandwich Islands. The British government's response was to dispatch a naval task force, and the aircraft carriers and sailed from Portsmouth for the South Atlantic on 5 April. The successful outcome of the war reaffirmed Portsmouth's significance as a naval port and its importance to the defence of British interests. In January 1997, Her Majesty's Yacht Britannia embarked from the city on her final voyage to oversee the handover of Hong Kong; for many, this marked the end of the empire. She was decommissioned on 11 December of that year at Portsmouth Naval Base in the presence of the queen, the Duke of Edinburgh, and twelve senior members of the royal family. Redevelopment of the naval shore establishment began