Following last month's successful test, the US now has the ability to shoot down intercontinental ballistic missiles (ICBM) targeting the homeland, according to the Pentagon.
The new evaluation represents an upgrade, as the Pentagon had previously said in a 2012 report that Washington only possessed a "limited ability" to protect the continental US from an enemy missile.
The remarks were made in a memo issued on Wednesday from the acting director of operational test and evaluation, David Duma, to Defence Secretary Jim Mattis, CNN reported.
The new assessment no longer describes the capability as "limited", according to the memo.
The operational test and evaluation office has changed its assessment of the system saying, "(Ground-based Midcourse Defence) has demonstrated capability to defend the US homeland from a small number of intermediate-range or intercontinental ballistic missile threats with simple countermeasures."
The memo attributes the upgrade to "initial data analysis" from last month's test, including "fixes" made to the "Kill Vehicle", which is the component that actually destroys the enemy missile, and the "sensors/command and control architecture".
The Pentagon successfully shot down an intercontinental ballistic missile using its upgraded long-range interceptor missile last month in what was widely seen as a test of the US' ability to counter a North Korean missile launch, reports CNN.
The Missile Defence Agency launched a ground-based interceptor from Vandenberg Air Force Base in California to intercept a US-launched mock ICBM target over the Pacific Ocean.
The test ICBM, which was equipped with decoys and flew thousands of miles per hour, was destroyed "thousands of miles off the coast" of the US mainland, with the intercept taking place northeast of Hawaii.