Story highlights The US successfully shot down a decoy missile in a test last month

Some experts caution that the missile defense system is still not fully developed

(CNN) Following last month's successful test, the US has the ability to shoot down intercontinental ballistic missiles targeting the homeland, according to a memo from the office of the Pentagon's chief weapons tester.

The new evaluation represents an upgrade, as the Pentagon office had previously said that the US only possessed a "limited ability" to protect the continental US from an enemy missile.

CNN obtained a copy of the memo from the acting director of operational test and evaluation, David Duma, to Defense Secretary Jim Mattis dated June 6, which has not yet been made public.

In a 2012 report, that same office said that the ballistic missile defense system had a "limited capability to defend the US homeland from small numbers of simple intermediate-range or intercontinental ballistic missile threats launched from North Korea or Iran."

The new assessment no longer describes the capability as "limited" according to the memo seen by CNN.

Read More