WASHINGTON (Reuters) - After a successful May test, the Pentagon has upgraded its assessment of its ability to defend the United States against incoming intercontinental ballistic missiles, like the ones North Korea is attempting to develop, according to a memo seen by Reuters on Wednesday.
The conclusion could add to the U.S. military's view that, although much more work remains on missile defence, it is staying ahead of a mounting threat from North Korea, which has declared its intent to develop an ICBM capable of striking the U.S. mainland.
Since 2012, the Pentagon's Director of Operational Test and Evaluation had assessed only that the United States had a "limited capability" to defend against a threat like the one from North Korea or Iran using interceptors in the Ground-based Midcourse Defense (GMD) programme, managed by Boeing Co.
But after successfully intercepting a simulated ICBM last month, the Pentagon office elevated that assessment, the memo, dated June 6, said.
"GMD has demonstrated capability to defend the U.S. homeland from a small number of intermediate-range or intercontinental missile threats with simple countermeasures," the memo said.
The May 30 missile test, which experts compare to hitting a bullet with another bullet, involved a simulated launch of a type of ICBM from the Kwajalein Atoll in the Marshall Islands.
The U.S. military then fired a missile to intercept it from Vandenberg Air Force Base in California. The test ended with a head-on strike, resulting in obliteration.
It was the first live-fire test against a simulated ICBM, which the military said was made even more complicated by the use of decoys designed to throw off the interceptor.
Previously, the GMD system had successfully hit its target in only nine of 17 tests since 1999. The last test was in 2014. However, the interceptor technology has been making steady advances. More tests are planned to advance U.S. defence capabilities.
Vice Admiral Jim Syring, the director of the Missile Defense Agency, told a hearing in Congress he still felt the defence programme needed improvement, even though his concerns about reliability had been addressed "in large part" in the past five to six years.
"It's just not the interceptor, the entire system," he said. "We are not there yet."
"We have continued work with the redesigned kill vehicle. We have continued work with the reliability of the other components of the system to make it totally reliable," he said. "We are not done yet."
At the same time, he assured he was confident in his ability to defend the United States.
The continental United States is around 9,000 km (5,500 miles) from North Korea. ICBMs have a minimum range of about 5,500 km (3,400 miles) but some are designed to travel 10,000 km (6,200 miles) or farther.
Syring said the ballistic missile defence review now underway would look not only at the capability of the current interceptors but whether more were needed.
"Where we need to be prudent and constantly vigilant on is what is the capacity increase we can expect from North Korea and what is our capacity needed to meet that threat," he said.
Additional reporting by David Brunnstrom; Reporting by Phil Stewart; Editing by James Dalgleish