November 12, 1968 Operations Building 3 at the National Security Agency (NSA) was dedicated.
When the Armed Forces Security Agency was established in 1949, and when it transformed into NSA in 1952, the communications intelligence (COMINT) and communications security (COMSEC) missions were conducted at different locations–COMINT at Arlington Hall Station, hosted by the Army, and COMSEC at the Naval Security Station. One of the purposes of the NSA move to Ft. Meade was the consolidation of NSA in one place. However, the rapid expansion of the COMINT function, requiring allocation of the Ft. Meade building almost entirely to COMINT left NSA’s missions still separated by a great distance. The predecessor to today’s lAD moved to Ops 3 in 1968.

Source: http://www.nsa.gov