The first evidence of a retractable landing gear design was in Europe circa 1911, but a working example didnt show up on aircraft until after WWI. As airplanes got heavier and faster, meanwhile, airport infrastructure-which mainly consisted of an open field and a windsock- couldnt keep up. As a result, some of the fastest airplanes in the 1920s and 1930s were seaplanes, even with the aerodynamic drag their floats imposed. By the time WWII erupted, the latest airplanes were equipped with retractable landing gear, even if in a conventional, taildragging configuration. Still, many long-range, multi-engine airliners of the day were seaplanes.