This watch, very rare and very special, was one of those sold by the American Forces to the Japanese Air Force in 1933. The dedication in Japanese on the case back says: "Air Force". The hour angle system was invented by Philippe Vanhorn Weems of the Annapolis Naval Academy, who was an authority in the 1920s and 30s. He trained the famous Charles A. Lindbergh, who set the record for the first non-stop transoceanic flight. This watch bears a large ball-shaped winding-crown, enabling the watch to be wound by a pilot wearing gloves. It is practically impossible to build a commercial timepiece which will keep time to the exact second under the conditions met in a ship or in an aeroplane. The unavoidable variation in the chronometer from true time necessitated an extra calculation in navigation to compensate for this chronometer error. Weems noted that in an airplane moving at speeds of 200 to 300 miles an hour or more, the time required for calculating chronometer error was a danger that should be eliminated. Since the high gear ratio made it impractical to set the second hand to the dial, Weems chose to set the dial to the hands. The seconds dial in the center of the watch is rotated by depressing the small stem. For navigation purposes, the Greenwich Mean time is indicated directly. The Longines Weems Watch is made in two models. The smaller model is useful not only for sea navigators and aircraft pilots, but particularly radio broadcasters as well as others, such as civil engineers who require exact time.