High Quality Content by WIKIPEDIA articles! The Northrop YF-23 or Northrop–McDonnell Douglas YF-23 was an American single-seat, twin-engine fighter aircraft designed for the United States Air Force (USAF). The design was a finalist in the USAF`s Advanced Tactical Fighter (ATF) competition, battling the Lockheed YF-22 for a production contract. Two YF-23 prototypes were built with the nicknames "Black Widow II" and "Gray Ghost".