FILE PHOTO: BF-3, a short take-off and vertical landing F-35 Lightning II, releases an inert 1,000 lb. GBU-32 Joint Direct Attack Munition (JDAM) separation weapon over water in an Atlantic test range in Patuxent River, Maryland August 8, 2012. REUTERS/Layne Laughter/Lockheed Martin/Handout

WASHINGTON (Reuters) - Lockheed Martin Corp LMT.N is being awarded a $423 million U.S. defense contract for cost-plus-fixed-fee modification to a previously awarded low-rate initial production Lot 10 F-35 Lightning II aircraft, the Pentagon said on Wednesday.