https://fas.org/nuke/guide/usa/airdef/an-fps-118.htm

OTH "over the horizon" defensive array– system for defense of missiles–operates without satellites

AN/FPS-118 Over-The-Horizon-Backscatter (OTH-B) Radar

The U.S. Air Force's over-the-horizon-backscatter (OTH-B) air defense radar system is by several criteria the largest radar system in the world. Six one-million-watt OTH radars see far beyond the range of conventional microwave radars by bouncing their 5-28-MHz waves off the ionosphere, an ionized layer about 200 km above the earth. It was developed over 25 years at a cost of $1.5 billion to warn against Soviet bomber attacks when the planes were still thousands of miles from US air space.

In 1970 Air Force Rome Air Development Center [RADC] engineers developed and constructed components for a frequency modulation/continuous wave (FM/CW) radar capable of detecting and tracking objects at over-the-horizon ranges. The radar installation and evaluation was accomplished on 15 September, while flight tests of a Beverage array antenna were completed on 30 September. On 30 October 1970 the radar and the Beverage array were integrated and operated as a single system for the first time.

The Department of Defense initially planned a central sector radar facing south, and an Alaska System facing north, to complement OTH-B radars on the east and west coast to detect enemy bombers and cruise missiles. With the end of the Cold War the military requirement for the central-sector radar had largely disappeared, and it was being pursued now almost exclusively for the drug interdiction mission. The Congress found this system to be redundant and unnecessary for this effort.

The total value of the ceiling price of that contract for the first and second sectors of the portion of the OTH-B radar program known as the Alaskan System was estimated at $530,000,000. The unexpected cost growth in the deployment of the first sector of the Alaskan OTH-B system defered procurement of the second sector of this system until at least fiscal year 1991. The main reason for the cost growth is the high cost of construction of this type of facility at the site selected by the Air Force. Consequently, the deployment of the Central CONUS system was deferred at least until fiscal year 1992, with land acquisition required no earlier than fiscal year 1991.