MAF is one of the largest manufacturing plants in the world with 43 environmentally controlled acres——under one roof, and it employs more than 4,200 people. From September 1961 to the end of the Apollo program in December 1972 the site was utilized by Chrysler Corporation to build the first stages of the Saturn I and Saturn IB, later joined by Boeing Corporation to build the first stage of the Saturn V rockets. From September 5, 1973, to September 20, 2010, the factory was used for the construction of the Space Shuttle's external fuel tanks by Martin Marietta Corporation, Denver Colorado.