The Tasman Bridge disaster occurred on the evening of 5 January 1975, in Hobart, the capital city of Australia's island state of Tasmania, when the bulk carrier Lake Illawarra, travelling up the Derwent River, collided with several pylons of the Tasman Bridge and caused a large section of the bridge deck to collapse onto the ship and into the river below. Twelve people were killed, including seven crew on board Lake Illawarra, and the five occupants of four cars which fell 45 metres (150 ft) after driving off the bridge. Hobart was cut off from its eastern suburbs, and the loss of the road connection had a major social impact. The ship's master was officially penalised for inattention and failure to handle his vessel in a seamanlike manner.

Hobart is the capital and most populous city of the island state of Tasmania, Australia. Home to almost half of all Tasmanians, it is the southernmost and least-populated Australian state capital city, and second-smallest if territories are taken into account, before Darwin, Northern Territory. Hobart is located in Tasmania's south-east on the estuary of the River Derwent, making it the most southern of Australia's capital cities. Its skyline is dominated by the 1,271-metre (4,170 ft) kunanyi/Mount Wellington, and its harbour forms the second-deepest natural port in the world, with much of the city's waterfront consisting of reclaimed land. The metropolitan area is often referred to as Greater Hobart, to differentiate it from the City of Hobart, one of the seven local government areas that cover the city. It has a mild maritime climate.