Northrop Grumman [NOC] sold the U.S. Air Force one of the company's test B-21 Raiders as part of an effort to accelerate production of the 6th generation stealth bomber. "To support the acceleration of aircraft deliveries, we agreed to sell an aircraft to the Air Force that was previously planned to be utilized as a company-owned test asset," John Greene, Northrop Grumman's chief financial officer, said on Tuesday during an earnings call. "The asset sale accelerated revenue into the quarter,…