The AN/FPS-118 Over-the-Horizon Backscatter Radar System (OTH-B) was developed in the 1970s and 1980s to provide all-altitude, long-range surveillance of aerial approaches to the United States. OTH-B radar systems use the ionosphere to refract outgoing radar waves and return signals, enabling the system to detect and track targets that would otherwise be hidden by the curvature of the earth, at ranges of up to 1,800 nautical miles. Original design configuration included plans for three OTH-B radar systems in the continental United States (East Coast, West Coast, and Central facing south) and one in Alaska. Each OTH-B system consists of an operations center, a receive site, and a transmit site, all geographically separated to prevent interference. They were to be coupled with a strengthened North Warning System (NWS), which runs along the north slope of Alaska and across the northern edges of Canada.
With the end of the Cold War, just months after their deployment, the OTH-B radars on the West Coast were placed in caretaker status, the Central and Alaska Systems were cancelled, and the East Coast system was redirected to counter-narcotics surveillance. Due to the high cost of operations, along with outdated technology, the East Coast system formally ceased radar operations in October 1997 and joined the West Coast system in caretaker status.
East Coast System
The East Coast operations center was located at Bangor Air National Guard Base, Bangor, Maine. It was transferred to the Maine Air National Guard for use as office space in 2004. The transmit site was located 13 miles northeast of Moscow, Maine. The property was sold in 2012 by GSA in a public auction. The receive site is located 9 miles north of Columbia Falls, Maine.
The West Coast operations center was located on Mountain Home Air Force Base, Idaho. It was transferred to the base for use as office space in 2005. The transmit site was located 17 miles east of Christmas Valley, Oregon. It was transferred to the state of Oregon in 2009. The receive site is located 35 miles southeast of Tulelake, California, in the Modoc National Forest.
Today, the remaining two sites are maintained in caretaker status until they can be sold, transferred, or otherwise disposed of. This effort is managed by ACC Acquisition Management and Integration Center (AMIC).