The U.S. Air Force said that it is considering reuse of the previous Over the Horizon Backscatter (OTH-B) radar sites to augment the U.S.-Canadian North Warning System (NWS).

In fiscal 2024 the Air Force requests more than $423 million for rapid prototyping of OTH-B to supplement NWS, including funds to satisfy a classified U.S. European Command requirement, $360 million to fund the first two OTH-B sites in the U.S., and funds for the detection of stratospheric balloons and unidentified aerial phenomena.

OTH-B is to have transmit and receive arrays 40 to 120 miles apart in four areas of the country–the Northeast, Northwest, Alaska and the South.

“Funds were added in FY24 to evaluate and develop improvements to the [OTH-B] sensors tracking algorithms to increase probability of detection of high altitude air vehicles such as stratospheric balloons and other unidentified aerial phenomena,” per the Air Force budget request.

Last month, Raytheon Technologies [RTX]-built AIM-9X Sidewinder missiles fired from fighter jets took down a Chinese surveillance balloon off the coast of South Carolina on Feb. 4 and three other unidentified objects off the coast of Alaska, in the Yukon territory of Canada and over Lake Huron (Defense Daily, Feb. 16).

On OTH-B, the Air Force is to conduct modeling for each proposed radar site to gauge the interaction of High Frequency Radar with the ionosphere in order to finalize OTH-B requirements.

The system would be a “back to the future” for the Air Force, which began looking into OTH-B in 1966. General Electric [GE] began developing a prototype for the then AN/FPS-118 OTH-B in 1975, but it was not until 1990-1991 that OTH-B was ready for fielding in Moscow, Maine; Columbia Falls, Maine; Christmas Valley, Ore.; and Tule Lake, Calif. The AN/FPS-118 OTH-B was to detect threats up to 1,800 miles away by bouncing signals off the ionosphere and then off of incoming targets. When the Soviet Union disbanded in 1991, the relevance of OTH-B for detecting Soviet bombers and low-flying cruise missiles receded, and the sites were eventually dismantled.

The Air Force increased its OTH-B funding request in fiscal 2024 “to account for continuation of component and material purchases, prototype antenna fabrication, and delivery for the first two radar sites,” the Air Force said in a March 29 email response to questions.

“Development of this capability is to extend the current North Warning System surveillance to long range early warning for North America in response to emerging threats,” the Air Force said. “Site selections for operation of the radars are ongoing and include evaluations for the feasibility of re-use of the previous OTH-B sites. Fielding of this capability will enable detection, tracking, and reporting of airborne and surface targets.”

The Air Force said in the fiscal 2024 budget request that threats to be addressed by OTH-B are airborne platforms as well as cruise missiles. The budget request says that OTH-B will have a “secondary and tertiary capability” against hypersonic missiles and ships.

Last year’s OTH-B appropriation was $12 million for theTactical Multi-Mission Over the Horizon Radar (TACMOR) to be based on the island of Palau to allow U.S. Indo-Pacific Command “to close gaps in surveillance coverage in key regions of the Pacific area of interest to the United States and its allies.”

Last December, California-based Gilbane Federal received a $118 million U.S. Navy contract to build reinforced concrete pads and foundations for TACMOR over the next three years on Palau.

The Air Force requests $5 million to finish TACMOR development in fiscal 2024.

U.S. Northern Command (NORTHCOM) has submitted a fiscal 2024 wish list that includes $55 million to accelerate testing for OTH-B to field OTH-B within the next five years rather than within a decade. That wish list also includes $211 million for nine long-range mobile radars to enable NORTHCOM to “plug the gaps when we have radar failures or to get after critical defense infrastructure, if tasked to do that,” NORTHCOM Gen. Glen Van Herck said this month.