The best-selling Boeing 737 jet started as a smaller, short-range jet and 19 737-200s jets were sold as T-43 Air Force trainers. Models 737-300, -400, and -500 jets were followed by the Next-Generation 737-600, -700, -800, -900 jets and the luxurious Boeing Business Jet. The Boeing Next-Generation 737s jets are the most advanced single-aisle airplanes in the market today. While these new airplanes retain the characteristics that made 737 jet classics so popular worldwide - reliable, simple and economical to operate - they underwent dramatic revisions. The 737-700 jet also is used for Project Wedgetail, an airborne early warning and control system for the Royal Australian Air Force, and for the U.S. Navy’s C-40A Unique Fleet Airlift Aircraft (NUFEA).