Funding for the $1.9 billion Homeland Defense Radar- Hawaii and a more than $1 billion Pacific radar that was expected to be located in Japan has been zeroed out in the Missile Defense Agency’s fiscal 2021 budget request — raising the possibility that neither radar will be built.

The emergence of hypersonic weapons that fly at least Mach 5 — five times the speed of sound or 3,800 mph, and which can maneuver around radars — has the Pentagon rethinking its sensor architecture and looking to space to cover radar gaps that exist on the ground.

Vice Adm. Jon Hill, director of the Missile Defense Agency, said at a press briefing Monday that “we realize we need to take another look at that architecture and so the secretary of defense has commissioned a study for us to look at the sensor architecture” specifically in the U.S. Indo-Pacific Command region.

Hill said the study will look at “what do we need to do and what other options do we have?”

The radar turn of events has occurred in a fast-changing environment with a host of missile advances by China, Russia, North Korea and Iran. Scrambling to maintain its military overmatch, the United States now is re-evaluating its missile defense lineup in Hawaii and elsewhere.

“Current global trends indicate that ballistic missiles, hypersonic glide vehicles and cruise missiles are becoming more and more capable,” Michelle Atkinson, the Missile Defense Agency’s director for operations, said at Monday’s press briefing for the agency’s $9.2 billion fiscal 2021 budget request.

Just last month the agency confirmed it had added the Pacific Missile Range Facility on Kauai to two locations on Oahu — Kaena Point and Kahuku Training Area — as candidate sites for the powerful Homeland Defense Radar- Hawaii.

The agency at the time said implementation was being pushed back from 2023 to the 2026 to 2028 timeframe.

The Kauai addition may be a last-ditch effort to get around mounting community and Native Hawaiian opposition on Oahu to build the radar, experts say. But the Hawaii radar is now not even mentioned in the agency’s new 15-page 2021 “budget estimates overview” for all its programs.

Meanwhile, the less-than-perfect $2 billion Sea-Based X-Band Radar, otherwise known as the “golf ball,” seems to have returned to a place of prominence in the Missile Defense Agency’s Pacific architecture.

While Hawaii possibly is losing a deep-look radar that can discriminate warheads from other rocket parts, it may be getting closer to gaining interceptor missiles dedicated to the protection of the state.

The Missile Defense Agency has increasingly acknowledged the capability of a new missile co-developed with Japan that has greater reach and speed, the SM-3 Block IIA, to defend against intercontinental ballistic missiles.

The agency now points to the ship- and shore-based missile as part of a possible “layered” homeland defense plan with 54-foot ground-based interceptors in Alaska and California taking the first shot at North Korean ICBMs, the 22-foot SM-3 IIAs there for a follow-up attempt and Terminal High Altitude Area Defense (THAAD) missiles as a last resort.

A key first flight test for the SM-3 IIA against a simple ICBM target is expected in May off the coast of Kauai using a Pearl Harbor destroyer to launch the interceptor missile.

“A lot is riding on the capability,” said Tom Karako, director of the Missile Defense Project at the Center for Strategic and International Studies. “There’s a lot of, I would say, hope this capability will be proven out, and if it does, it opens up a lot of flexibility.”

Riki Ellison, chairman of the nonprofit Missile Defense Advocacy Alliance, believes it is now “inevitable” that Hawaii will get added ICBM protection in the form of destroyers armed with SM-3 IIA missiles, or activation of the Aegis Ashore test site at the Pacific Missile Range Facility in times of emergency with the new missile.

In the short term, the Pentagon is “assuming greater risk for Hawaii” without the Homeland Defense Radar-Hawaii, which would have been able to see out in volume and depth, Ellison said.

“It was a tremendously capable radar that would have reduced the (missile) risk to Hawaii,” he said.

Ellison has long maintained that Hawaii is under-defended. Guam has a THAAD system protecting it from shorter range North Korean missiles.

Although officials stress that Hawaii is protected by 44 ground-based missiles in Alaska and California, it is quite literally a longshot for the system, with many of the missiles earlier first- generation interceptors, according to Ellison.

Additional demand for those defensive missiles will increasingly come from Iranian threats, he said.

In the meantime, the Pacific has AN/TPY-2 radars, Aegis ship radars and the SBX that handle the sensor load, the Missile Defense Agency’s Hill said. All are less capable than the Homeland Defense Radar- Hawaii.

The budget request calls for 305 days at sea and 60 days for in-port maintenance in 2021 for the SBX, which is limited by a narrow field of view likened to looking through a soda straw.

Hill said the Pacific radar was being delayed because of unspecified “host nation issues that we have to comb through.”

He added that the “Pacific radar is no longer in our budget. We’ve moved it out and I can’t tell you where (funding for it) goes because I don’t know. It goes to other (Defense Department) priorities.”