page_title: Over-the-horizon radar
section_title: U.S. Navy
hierarchical_section_title: Over-the-horizon radar / Systems / U.S. Navy
caption_attribution_description: Range of the Relocatable Over-the-Horizon Radar stations of the US Navy
context_page_description: Over-the-horizon radar, sometimes called beyond the horizon, is a type of radar system with the ability to detect targets at very long ranges, typically hundreds to thousands of kilometres, beyond the radar horizon, which is the distance limit for ordinary radar. Several OTH radar systems were deployed starting in the 1950s and 1960s as part of early warning radar systems, but these have generally been replaced by airborne early warning systems. OTH radars have recently been making a comeback, as the need for accurate long-range tracking becomes less important with the ending of the Cold War, and less-expensive ground-based radars are once again being considered for roles such as maritime reconnaissance and drug enforcement.
context_section_description: The United States Navy created their own system, the AN/TPS-71 ROTHR (Relocatable Over-the-Horizon Radar), which covers a 64-degree wedge-shaped area at ranges from 500 to 1,600 nautical miles (925 to 3,000 km). ROTHR was originally intended to monitor ship and aircraft movement over the Pacific, and thus allow coordinated fleet movements well in advance of an engagement. In 1991, a prototype ROTHR system was installed on the isolated Aleutian Island of Amchitka, Alaska, monitoring the eastern coast of Russia. It remained in use until 1993, and the equipment was later removed into storage. The first production systems were installed in the test site in Virginia for acceptance testing, but were then transitioned to counter the illegal drug trade, covering Central America and the Caribbean. The second production ROTHR was later set up in Texas, covering many of the same areas in the Caribbean, but also providing coverage over the Pacific as far south as Colombia. It also operates in the anti-drug trafficking role. The third, and final, production system was installed in Puerto Rico, extending anti-drug surveillance past the equator, deep into South America.
caption: Coverage of the three U.S. Navy ROTHR stations in Texas, Virginia, and Puerto Rico
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