 Modelled on the Milford Proving Ground operated by General Motors (GM) in Michigan, Millbrook was opened in the 1960s by the GM subsidiary Bedford before passing over to Vauxhall.Due to the geographical needs of a full testing centre, including both hills and flat land, the traditional choice of a former Royal Air Force airfield was ruled out and many sites around the UK were surveyed before the location at Millbrook was decided upon, especially due to having the benefit of being close to Vauxhall's production site at Luton.Construction of the Proving Ground began in 1968, and once the facility opened in 1970 it acted as the testing site for many European GM models from, among others, the Vauxhall and Bedford companies.