FILE PHOTO: A US Marine Corps Lockheed Martin F-35B fighter jet taxis after landing at the Royal International Air Tattoo at Fairford, Britain July 8, 2016. REUTERS/Peter Nicholls

WASHINGTON (Reuters) - Lockheed Martin Corp was awarded a $506.9 million modification to a U.S. defense contract for a guided missile system and associated services, the Pentagon said on Thursday.