The AN/FSQ-7 Combat Direction Central, referred to as the Q7 for short, was a computerized command and control system for Cold War ground-controlled interception used in the USAF Semi-Automatic Ground Environment (SAGE) air defense network. The name “AN/FSQ” derives from Army-Navy / Fixed Special eQuipment. An advancement of the pioneering MIT Whirlwind II digital computer design, and manufactured by IBM as prime contractor, the AN/FSQ-7 was the largest discrete computer system ever built. Each of the 24 installed machines weighed 250 tons. The AN/FSQ-7 used a total of 60,000 vacuum tubes (49,000 in the computers) and up to 3 megawatts of electricity, performing about 75,000 instructions per second for networking regional radars. Primary functions Installations in the USAF Semi-Automatic Ground Environment (SAGE) air defense network were configured as duplex systems, using a pair of AN/FSQ-7 computers to provide fault tolerance. One was active at any time, the other on standby. The standby system copied data from the active system to minimize switchover time if needed. A scheduled switchover took place every day. The AN/FSQ-7 calculated one or more predicted interception points for assigning manned aircraft or CIM-10 Bomarc missiles to intercept an intruder using the Automatic Target and Battery Evaluation (ATABE) algorithm. Also used in the Nike AN/FSG-1 system, ATABE automated the Whiz Wheel (Felsenthal CPU-73 A/P Air Navigation Attack Computer) method used in manual command post operations. The Q7 fire button launched the Bomarc, and an additional Q7 algorithm automatically directed the missile during climb and cruise to the beginning of its supersonic dive on the target when guidance transferred to the missile seeker system for the homing dive. Later improvements allowed transmission of Q7 guidance to autopilots of manned fighters for vectoring to targets via the SAGE Ground to Air Data Link Subsystem (cf. bomber vectoring to a Bomb Release Point in 1965–1973 Vietnam via vacuum-tube analog computers.) History The first United States radar network used voice reporting to the 1939 Twin Lights Station in New Jersey, and the post-World War II experimental Cape Cod System used a Whirlwind I computer at Cambridge, Massachusetts to network long-range and several short-range radars. The key Whirlwind modification for radar netting was the development of magnetic-core memory that vastly improved reliability, doubled operating speed, and quadrupled input speed relative to the original Williams tube memory of the Whirlwind I. The AN/FSQ-7 was based on the larger and faster (but uncompleted) Whirlwind