The AN/FPS-27 Radar was a Long Range search radar used by the United States Air Force Air Defense Command. Westinghouse built an FD search radar designed to operate in the S-band at 2322 to 2670 MHz. The radar was designed to have a maximum range of 220 nautical miles and search to an altitude of 150,000 feet. In the early 1970s, AN/FPS-27 radar stations that had not been shut down received a modification (solid state circuitry replacing vacuum tubes) that improved reliability and saved on maintenance costs.