The United States’ plan for new early warning radars to safeguard the homeland is moving closer to realization.
The U.S. Air Force, in a notice published in the Federal Register, said that environmental impact statements are being prepared for the construction of over-the-horizon (OTHR) radar systems. The notice listed one site each in Idaho and Nevada and three in Oregon as possible locations, according to an April 2025 report by the website Breaking Defense.
OTHR enables the long-range detection of threats by bouncing radio waves off the Earth’s ionosphere — which starts about 80 kilometers above the surface — and beyond the planet’s curvature, according to an April report by Air & Space Forces Magazine. This allows OTHR to detect aircraft, cruise missiles and surface ships that could operate “under the radar” of more conventional systems, the magazine said. The U.S. military has decades of research and development in OTHR technology. The proposed next-generation system would augment current ones such as the Navy’s Relocatable Over-the-Horizon Radar (ROTHR) that has sites in Virginia and Texas devoted to drug-smuggling interdiction and early warning for Naval vessels, according to a March 2021 story by Military & Aerospace Electronics magazine.
Defense officials say the U.S. faces growing threats from strategic competitors’ development of hypersonic weapons, long-range cruise missiles and even fractional orbital bombardment systems.
The notice in the Federal Register said the Air Force could acquire land from the five listed locations to build two OTHR systems, according to Breaking Defense. The environmental reviews are expected to take two years, according to the notice.
OTHR would boost “long-range, early detection capability of airborne threats that may be obscured from conventional line-of-sight radar systems by the curvature of the Earth,” the notice stated. “These threats are difficult to detect and can strike with limited warning, which reduces the time and response options available to our national leaders.”
The capability to quickly identify and respond to threats is a key to deterrence. U.S. military leaders such as Air Force Gens. Anthony Cotton and Gregory Guillot emphasize the importance of OTHR and other systems to provide domain awareness.
Gen. Cotton commands U.S. Strategic Command (USSTRATCOM), whose global mission includes strategic deterrence. Gen. Guillot commands U.S. Northern Command (USNORTHCOM) and the North American Aerospace Defense Command (NORAD).
NORAD is the binational Canadian-U.S. organization tasked with aerospace warning, aerospace control and maritime warning for North America. USNORTHCOM executes homeland defense and civil support.
In April 2025, Gen. Guillot told U.S. lawmakers that OTHR are “critical to continental defense,” forming, alongside other systems, the “foundation for the Golden Dome construct” — the White House-mandated initiative for a comprehensive missile shield, according to Air & Space Forces Magazine.
In March 2025, Canadian Prime Minister Mark Carney said his nation’s contribution to continental defense will be OTHR systems purchased from Australia along with an expansion of military operations in the Arctic, according to The Associated Press (AP). Carney’s office said the $4.2 billion system will provide early warning coverage from the Canada-U.S. border up into the Arctic, the AP reported. The Arctic OTHR is part of a larger initiative to modernize the radar capabilities the country provides to NORAD.
Because OTHRs can see beyond the curvature of the earth, they could help detect threats such as low-flying cruise missiles launched over the North Pole.
“Canada will work closely with the United States to ensure the interoperability of Canadian and U.S. solutions to strengthen domain awareness in North America’s approaches in support of the NORAD mission,” a Canadian Department of National Defence spokesperson told Breaking Defense.