A sailor’s computer input error on the Pearl Harbor-based destroyer USS John Paul Jones apparently caused an $80 million missile defense test failure off the coast of Kauai on June 21, according to DefenseNews.com

A medium-range ballistic target missile was launched that night from the Pacific Missile Range Facility on Kauai. The John Paul Jones, used as a test bed for missile defense, detected and tracked the target missile with its onboard AN/SPY-1 radar using the Aegis Baseline 9.C2 weapon system, the U.S. Missile Defense Agency said.

After acquiring and tracking the target, the ship launched an SM-3 Block IIA guided missile, but the interceptor — a new missile being jointly developed with Japan — did not hit the target, the agency said. No immediate cause for the failure was given at the time.

A Missile Defense Agency review found that a mistaken input caused the SM-3 missile to self-destruct, DefenseNews reported Monday.

“A tactical datalink controller, in charge of maintaining encrypted data exchanges between ships and aircraft, accidentally identified the incoming ballistic missile target as a ‘friendly’ in the system, causing the SM-3 missile to self-destruct in flight,” the news organization said.

Contacted by the Honolulu Star-Advertiser, the Missile Defense Agency did not pinpoint fault.

“Though the review is still in process, the SM-3 IIA interceptor and Aegis Combat System have been eliminated as the potential root cause. We are conducting an extensive review as part of our standard engineering and test processes, and it would be inappropriate to comment further until we complete the investigation,” Air Force Lt. Gen. Sam Greaves, the agency’s director, said in an email.

The failure was divulged as tensions mount with North Korea, which is reportedly readying a second Hwasong-14 intercontinental ballistic missile test. The Missile Defense Agency, meanwhile, is expected to conduct another test of the Terminal High Altitude Area Defense system between Hawaii and Alaska over the weekend.

The total cost for the June 21 flight test, including test execution, site preparation and the test target, was approximately $80 million, Greaves said.

“Live fire flight tests are the best opportunity we have to exercise our systems in a realistic environment, and this test provided an opportunity to gather critical flight data, test our processes and conduct valuable crew training,” he said. “This exercise resulted in data and lessons that we otherwise would not have been able to gather, and it will ultimately improve our operational procedures. I remain completely confident in SM-3 IIA and Aegis (ballistic missile defense) programs.”

Riki Ellison, chairman of the nonprofit Missile Defense Advocacy Alliance, confirmed that the failed intercept was due to “operator error.”

“Won’t pinpoint a sailor — as it was not singular and there had to be oversight as well,” he said in an email. “The test was not a failure as the missile performed what they needed to see to move forward with a limited production.” He added that “it was a faulty procedure that will now be adjusted in a new policy procedure that will prevent this” from happening again.

The new policy will apply to all ships with ballistic missile shoot-down capability, “thereby saving critical failures in the field of combat if used,” Ellison said.

Asked whether any action was taken against sailors involved in the apparent mistake, Navy Region Hawaii referred questions to U.S. Pacific Fleet’s Naval Surface Force in San Diego, which did not provide comment Tuesday.

The SM-3 IIA missile is seen as having implications for the defense of Hawaii from North Korean ICBMs.

With growing concern over Hawaii’s potential vulnerability, plans are being fast-tracked for a new $1 billion medium-­range radar by 2023, while the Missile Defense Agency recently confirmed that the SM-3 IIA could add a second layer of defense for the state.

Thirty-six ground-based interceptors in Alaska and California defend Hawaii — and the mainland — against North Korean missiles. However, Hawaii’s proximity to North Korea — 4,660 miles — means an enemy missile could arrive in just 20 minutes and limits what officials call a “shoot, look, shoot” second chance for success.

Ellison is among a growing number of voices calling for activation of the $450 million Aegis Ashore missile defense testing facility on Kauai in times of emergency with current SM-3 1B missiles and, as soon as possible, the even more capable SM-3 IIAs.

An intercept test conducted in February off Kauai using the John Paul Jones and an SM-3 IIA missile was successful. The missile will be used to protect Japan, Romania and Poland from ballistic missile threats, and is expected to be test-fired from Aegis Ashore on Kauai by the end of the year.

In a separate test a ballistic missile target simulating an intermediate-range North Korean threat that was launched by a C-17 cargo aircraft north of Hawaii was successfully intercepted July 11 by a defensive missile in a test of the mobile THAAD system. The THAAD battery is temporarily located in Kodiak, Alaska.

THAAD batteries are globally transportable and rapidly deployable. The system has a perfect track record of 14 flight intercepts in 14 tests.

Missile experts say North Korea’s successful July 3 ICBM flight test showed it could hit Hawaii.

Adm. Harry Harris, head of U.S. Pacific Command, recently told the Star-Advertiser that “that’s just the missile, and so, you have to mate a nuclear warhead to that missile. I know that (North Korean leader) Kim Jong Un has stated his intent to do that, and at some point he probably will.”

Harris said he believes Hawaii needs to have a “phased approach” to its defense.

“We have to have a defense-of-Hawaii radar first, and that’s in the plan. That’s being funded, and I think it’s a great thing,” he said. “And I’ve called for a study to determine what the follow-on should be to go with that radar (and) whether it should be an Aegis Ashore or THAAD” or some other defense.