Boeing began designing the 737 in 1964. The very first 737-100 flew in 1967. It was first used by an airline in February 1968. The 737-200 started being used in April 1968. The -200 was basically just a longer version of the 737-100. In the 1980s Boeing made the -300, -400, and -500 models. Boeing called these models the Boeing 737 Classic series. The 737 Classics could carry more passengers, and they had new engines: CFM56 turbofans. The 737 Classic planes also had some improvements made to the wings. In the 1990s, Boeing brought out the 737 Next Generation. The 737 Next Generation planes also had redesigned wings, a better cockpit and a new cabin. The 737 Next Generation is made up of the -600, -700, -800, and -900ER models. These models go from to in length.