WASHINGTON (CNN) -- U.S. Navy ships capable of shooting down ballistic missiles are being moved to the Sea of Japan, a Navy spokesman said. The USS Chaffee is one of two destroyers headed to South Korea for an upcoming ceremony. The USS Chaffee is one of two destroyers headed to South Korea for an upcoming ceremony. The move came as North Korea was preparing for an expected rocket launch next month. Later Thursday, Japan announced it was ready to fire on the rocket if any part of it enters Japanese airspace.