ROBERT BURNS
Associated Press

WASHINGTON  — Hit or miss, the Pentagon’s attempt Tuesday to shoot down a mock warhead over the Pacific Ocean marks an important milestone for an oft-criticized defense program that could be what stands between an incoming North Korean strike and the United States.

The $244 million test will not confirm that the U.S. is capable of defending itself against an intercontinental ballistic missile fired by North Korea, even if it is successful.

Pyongyang also is understood to be moving closer to the capability of putting a nuclear warhead on such a missile and could have developed decoys sophisticated enough to trick an interceptor into missing the real warhead.

The most recent U.S. missile intercept test, in June 2014, was successful, but the longer track record is spotty. Since the system was declared ready for potential combat use in 2004, only four of nine intercept attempts have been successful.

“This is part of a continuous learning curve,” said Navy Capt. Jeff Davis, a Pentagon spokesperson.

“We improve and learn from each test, regardless of the outcome,” he said. “We look forward to understanding the results so we can continue to mature the system and stay ahead of the threat.”

The Pentagon is still incorporating engineering upgrades to its missile interceptor, which has yet to be fully tested in realistic conditions. A test failure Tuesday would raise new questions about the defensive system but would be unlikely to compel the Pentagon to abandon plans to expand it.

North Korea says its nuclear and missile programs are a defense against perceived U.S. military threats. Its accelerating missile development has complicated Pentagon calculations, most recently by incorporating solid-fuel technology into its rockets. The step would mean even less launch warning time for the U.S. Liquid fuel is less stable and rockets using it have to be fueled in the field, a process that takes longer and can be detected by satellites.

North Korea’s latest act Monday involved firing a short-range ballistic missile that landed in Japan’s maritime economic zone.

In Tuesday’s scheduled test, the Pentagon’s Missile Defense Agency plans to launch an interceptor rocket from an underground silo at Vandenberg Air Force Base in California. The interceptor’s target would be an intercontinental ballistic missile fired from a test range on Kwajalein Atoll, part of the Marshall Islands in the Pacific.

If all goes as planned, a 5-foot-long “kill vehicle” released from atop the interceptor will zero in on the ICBM-like target’s mock warhead outside Earth’s atmosphere and obliterate it by sheer force of impact. The “kill vehicle” carries no explosives, either in testing or in actual combat.

The planned target is a custom-made missile meant to simulate an ICBM, meaning it will fly faster than missiles used in previous intercept tests, according to Christopher Johnson, the Missile Defense Agency’s spokesperson. The target is not a mock-up of an actual North Korean ICBM, and details of its exact capabilities have not been made public.

The Pentagon likens the defensive tactic, officially known as the Ground-based Midcourse Defense system, to hitting a bullet with a bullet. With congressional support, the Pentagon is increasing by the end of this year the number of deployed interceptors, based in California and Alaska, to 44 from the current total of 36.

While Tuesday’s test wasn’t designed with the expectation of an imminent North Korean missile threat, the military will closely look for progress toward the stated goal of being able to reliably shoot down a small number of ICBMs targeting the United States. The Pentagon is thirsting for a success story amid growing fears about North Korea’s escalating capability.

Laura Grego, senior scientist at the Union of Concerned Scientists, which has criticized the missile defense program, calls the interceptor an “advanced prototype,” meaning it is not fully matured technologically even if it has been deployed and theoretically available for combat since 2004. A successful test Tuesday, she said, may demonstrate the Pentagon is on the right track with its latest technical fixes.

“Overall,” she wrote in an analysis prior to the test, the military “is not even close to demonstrating that the system works in a real-world setting.”

The interceptors are, in essence, the last line of U.S. defense against an attack by an intercontinental ballistic missile.

The Pentagon has other elements of missile defense proven to be more reliable, although they are designed to work against medium-range or shorter-range ballistic missiles. These include the Patriot missile, which numerous countries have purchased from the U.S., and the Terminal High Altitude Area Defense, or THAAD, which the U.S. deployed this year to South Korea to defend against medium-range missiles from North Korea.