Stopping a North Korean missile with US defense system is no sure thing, tester says

The United States' $36 billion system of ground-based interceptors can't yet be counted on to shoot down a nuclear-armed missile aimed at the West Coast by the likes of North Korea or Iran, the Pentagon's weapons testing office says.

The network of radar and communications combined with missiles based in California and Alaska has demonstrated only a "limited capability to defend the U.S. homeland from small numbers of simple" intercontinental ballistic missiles, the testing office said in its latest annual report.

Despite international sanctions, North Korea has continued to test nuclear bombs and the missiles that might eventually carry a miniaturized warhead to the continental U.S. Meanwhile, the U.S. has criticized Iran for conducting ballistic missile tests, although the Islamic Republic has said its program is defensive and isn't designed to carry nuclear warheads.

The probability that the U.S. would succeed in intercepting an incoming missile can't be quantified with any precision "due to a lack of ground tests" supported by verified "modeling and simulation," according to an advance copy of the assessment provided late Monday to congressional defense committees and Pentagon officials.

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The testing office's assessment is the same as its 2016 report because too few new results were generated to warrant a change, even as the threat from North Korea in particular has grown.

The office said the "reliability and availability of the operational" interceptors is also low, as the Missile Defense Agency continues to discover new flaws and "failure modes" during testing.

In response, Vice Adm. James Syring, director of the missile defense agency, said in an interview Monday he retains "high confidence" in the system. He said the next attempt to intercept a dummy missile is tentatively scheduled for the period of April to June.

With North Korean ruler Kim Jong Un saying his country is in the "last stage" of preparations to test-fire an ICBM, President-elect Donald Trump may face a more urgent challenge than predecessor Barack Obama in dealing with the regime. Christopher Hill, a former senior U.S. diplomat for talks with North Korea, said on Saturday he believed Pyongyang would be able to claim with credibility within four years that it can hit the U.S. with a nuclear weapon.

"It won't happen!" Trump wrote recently on Twitter of North Korea's potential test.

Success in the next U.S. missile-defense test might bolster Trump's vow that North Korea can be stopped. A test failure would deal him a public relations embarrassment.

The next test will attempt to shoot down a target that replicates for the first time the speed, trajectory and closing velocity of an actual ICBM, Syring said. The U.S. will test avionics updates to the booster rocket built by Orbital ATK Inc. that carries an improved version of a hit-to-kill conventional warhead built by Raytheon Co.

Interceptors are located at Fort Greely in Alaska and Vandenberg Air Force Base in California. The system is managed by Boeing.

The next interception attempt will be the first since a successful test in June 2014. Before that, though, two tests that failed in 2010 prompted an extensive effort to fix flaws with the interceptor's warhead that Syring said have now been fixed and verified.

Syring said he has high confidence in the system because many of the interceptors in silos today are tipped with the same model warhead that was tested in 2014. Success in the next round would trigger the installation of eight more interceptors in Alaska, for a total of 44 — a goal set by former Defense Secretary Chuck Hagel.

"I am very confident in the systems and procedures" the U.S. Northern Command, which operates the missile defense shield, "will employ to intercept a North Korean ICBM were they to shoot it toward our territory," Syring said.

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Laura Grego, a missile defense analyst with the Union of Concerned Scientists, said last year that none of the interception tests since 2010 have used targets representative of actual threats or complex countermeasures.

Since its inception, the system "has destroyed its target fewer than half the 17 times it has been tested, and its record is not improving over time," she said. Since the 2004 deployment decision, "the system has a three-for-nine record," said Grego, co-author of a July 2016 report titled "Shielded From Oversight: The Disastrous U.S. Approach to Strategic Missile Defense."

Bloomberg's Rosalind Mathieson contributed.