Sometime yet this fall, the U.S. Missile Defense Agency said it plans to test for the first time a new, mainly ship-based interceptor against an intercontinental-range ballistic missile target in a “defense of Hawaii” scenario.

If successful, the test will move what’s known as an “underlay” defense one step closer to reality for the Aloha State.

The key missile intercept was delayed from the spring with the onset of COVID-19.

Meanwhile, Congress and the Pentagon continue a tug of war over the necessity of a $1.9 billion Homeland Defense Radar-Hawaii that may or may not be built at the Pacific Missile Range Facility on Kauai.

A Missile Defense Agency PowerPoint slide for the upcoming test shows a mock ICBM launched from Kwajalein Atoll, the rocket arcing over Hawaii — with an advanced SPY-6 air and missile radar on Kauai to help track it — and a U.S. Navy destroyer somewhere between Hawaii and California firing an SM-3 Block IIA missile to intercept it.

Hawaii has limited protection from 44 big ground-based interceptors mainly in Alaska but also California that protect the United States — and have to travel very long distances to intercept a North Korean missile headed for Hawaii.

The smaller SM-3 IIAs would be one more line of defense in Hawaii’s backyard.

Although a lot of focus now is on China, the Center for Strategic and International Studies noted that “North Korea’s ballistic missile program is a rapidly-developing threat to global security.”

The worries that prompted a mistaken Jan. 13, 2018, alert warning of a ballistic missile inbound to Hawaii haven’t gone away.

Adm. Phil Davidson, head of U.S. Indo-Pacific Command on Oahu, told the Missile Defense Advocacy Alliance in September that “North Korea, as long as they retain the capability to shoot long-range missiles and to continue to develop nuclear weapons, will remain, really, in my view, our most immediate threat.”

China, meanwhile, is the most significant strategic threat for the United States in the 21st century, he said.

The 2018 National Defense Authorization Act requires for the “defense of Hawaii” test no later than Dec. 31 of an SM-3 Block IIA missile to defeat a simple — meaning no counter- measures — ICBM-representative threat.

“The congressional language says to do a defense-of-Hawaii scenario. Do it with a ship and do the feasibility of the SM-3 Block IIA. The test is constructed right now to exactly do that,” Vice Adm. Jon Hill, director of the Missile Defense Agency, said in August during a Heritage Foundation interview.

The United States has a range of missile defenses: Patriot, Terminal High Altitude Area Defense and Aegis ship-based systems that can defeat North Korean short- to intermediate-range ballistic missiles.

The 54-1/2-foot ground-based interceptors have a range of 3,728 miles compared with 994 miles for the 22-foot SM-3 IIA and 124 miles for 20-foot THAAD missiles, according to the Missile Defense Agency.

Hill said the SM-3 IIA will be stressed “outside its design space. It was designed for medium and intermediate range (threats),” he said. “Now we’re going against a long-range intercontinental ballistic missile. The analysis says we’ll be successful, but nothing is real to any of us until we actually get the credible data from being out at the flight range.”

In February the agency said six SM-3 IIA missiles were being sought in fiscal 2021, for a total of 60 procured.

The missiles are being secured as the Defense Department pursues regional missile systems to provide a layered homeland defense.

Hill said Patriot can be thought of as an ability to defend a city, THAAD to defend a state and Aegis with the SM-3 able to defend a region, while the big ground-based missiles defend the country.

“You can imagine those as bubbles of protection, or a shield across the country,” Hill said. “To me it’s a no-brainer to have that sort of defensive depth.”

If the upcoming SM-3 IIA test goes well, “that allows us to now start to think through that architecture and start working more closely with war-fighters to determine where they would position the ship” for the defense of Hawaii, the mainland or Guam, Hill said.

Another route to additionally protect Hawaii is using the Aegis Ashore Missile Defense Test Center on Kauai — which has fired an SM-3 IIA missile before.

The Pentagon previously said it would evaluate operationalizing the Pacific Missile Range Facility site to see whether it was a viable near-term option. The Missile Defense Agency reported in February the test site could be temporarily activated in the event of a national emergency for missile defense.

In a somewhat contradictory stance, the Navy wants to keep PMRF for testing only but also doesn’t want to relegate some of its ships to ballistic missile defense duty, preferring to see that job shifted to shore sites.

The future of the Hawaii radar also is unclear. Funding was zeroed out in the Missile Defense Agency’s 2021 budget request with the Pentagon rethinking its sensor architecture and looking to space to cover radar gaps that exist on the ground. The Senate Armed Services Committee added money back in for the Hawaii radar.

In August, Hill talked about the emerging challenges of maneuvering hypersonics and cruise missiles.

“You’ve got to look in space for a ballistic target. Hypersonics (are) right on the edge of the atmosphere, and cruise missiles are going to be down low,” Hill said. “So you have to be able to do that 360 coverage from surface up through space if you’re going to be successful against the convergent threat.”

“And so when you talk about sensors on Hawaii, you know, I spent a lot of time out there when we were first siting” the big radar, and the Defense Department “made a decision” about priorities, he said.

Hill talked about the formidable nature of the threats and said that “we need global coverage.”

“If you’re going to have a maneuvering threat that’s unpredictable, you need to be up high looking down,” he said. “And that’s really the only way to get global coverage, is from space.”

As a result, the Defense Department “had to make some hard decisions: Do we stop-gap here with another terrestrial-based sensor, or do we go to space? And so it was a really tough decision. It’s still a discussion today (in Congress). I don’t know how that’s going to play out.”

Mark Wright, a Missile Defense Agency spokesman, said using funds appropriated in fiscal 2020, the agency continues limited planning and siting activities for the Hawaii radar.

The agency has postponed resuming an environmental impact statement “while we continue to work with the (Defense Department) to evaluate the best solution to meet the war- fighters’ requirements,” he said.