The flying boat is a unique form of aircraft, with the ability to operate from sea or river and, in amphibian form, from land too. Over 100 types of British flying boat and amphibian were built during a 40-year period from the days of the pioneer airmen to the advent of the jet engine. Early attempts at flying from water were sometimes fraught, but during World War I the practical military flying boat was steadily developed, serving with the Royal Naval Air Service as an important component in the campaigns waged against the naval forces of Imperial Germany - particularly her U-Boats. The inter-war period witnessed the growth in prominence of civil flying boats as commercial air routes became established worldwide. Light civilian flying boats were produced for use by private owners and modest operators, while the military flying boats of the RAF were many and varied. During World War II the flying boat defended Britain's sea routes around the globe with great success, and British examples were also employed by many of the Allied nations. Yet after the war, the type faded from widespread use and, despite resistance from enthusiasts, by the mid-1950s they had all but disappeared.