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).