By Emily Atkin (October 24, 2013, 6:59 PM EDT) -- The award for most costly contract this week was bestowed upon United Technologies Corp.'s U.S.-based aerospace manufacturer Pratt & Whitney, which snagged a $508 million modification for low-rate production of F-35 takeoff and landing aircrafts, the U.S. Department of Defense announced Wednesday. The modification calls for 18 conventional takeoff and landing aircrafts for the U.S. Air Force, six short takeoff and vertical landing propulsion systems for the U.S. Marine Corps and seven carrier variant propulsion systems for the U.S. Navy. The contract also calls on UTC to provide two propulsion systems for Italy, three for Australia and one for Italy. The work is expected to be completed in June 2016, the DOD said....