MAF is one of the largest manufacturing plants in the world with 43 environmentally controlled acres (m2 (sq ft)) under one roof, and it employs approximately 3,700 people. From September 1961 to the end of the Apollo program in December 1972 the site was utilized by Chrysler Corp to build the first stages of the Saturn I and Saturn IB, later joined by Boeing Corp to build the first stage of the Saturn Vs. From September 5, 1973 to September 20, 2010 it was used for the construction of the Space Shuttle's external fuel tanks by Martin Marietta Corp., Denver Colo.