The BRN-3 satellite navigation system.  Hard to believe, but the US had a relatively sophisticated, world-wide GPS system in the 1960’s.  It was called the Transit System then.  We could only get fixes at multi-hour intervals, because there was only a few birds in orbit then.  The accuracy was darned good though, even by today’s standards.  This equipment has grown a fifth cabinet from previous marks.  Note the safe atop the cabinet on the left used to securely store the crypto tapes used to decode the encrypted signals from the Transit satellites, required to achieve military level accuracy.  The curtains at the right were used to obscure the goings on of the Navy techs who loaded the tapes.  One of the reasons a Top Secret Crypto clearance was required to work in NIC.