In the second half of the 1930s and early 1940s, a group of American firms continued developing sunglasses. The military "flying sun glasses (comfort cable)" were standardized in November 1941. They were produced in huge quantities (several million pieces) for pilots and sailors. The lenses were made to a joint standard shared by the U.S. Army Air Corps and the U.S. Navy. As a result, the lens carried an "AN" (Army/Navy) specification number: the AN6531. The U.S. Government specified the shape of the lens and the color, which was initially a green tinted lens that transmitted 50% of incoming visible daylight. This AN6531 Type 1 lens proved insufficient to protect pilot's eyes from sun glare so this lens was superseded by the darker AN6531 Type 2 lens in rose smoke. Various contractors made the frames and ground the lenses. These included American Optical, Bausch & Lomb, The Chas. Fischer Spring Co., Willson Optical and Rochester Optical Co. Frame and hinge design varied slightly from contractor to contractor.
