Complexes 31 and 32 were built between July 1959 and July 1960 to support the Air Force's Minuteman missile program. Each complex had one blockhouse and two launch pads. The two "A" pads were constructed as conventional flat pads, and the two "B" pads were built as ballistic missile silos. The sites were modified subsequently to support later versions of the Minuteman missile. In all, 92 Minuteman I, II and III missiles were launched from the complexes between 1 February 1961 and 15 December 1970.