This particular example was delivered to the Czeck Air Force in 1938 on the eve of the second World War. Available as a non-military issed watch since 1939 as well, the watch was equipped with three different calibers: 15.94, 15.26 and 15.68. It is interesting to note that the accompanying correspondance with Longines confirms that the military issue number 2550 found on the outer caseback was made at the Longines factory. The early pilot watches represent an important milestone in the development of flight watches with their inner revolving bezel and are rarely found in their original condition.