U.S. Army MI-I-5 Optical Gas Mask
The U.S. MI-I-5 Optical Gas Mask was developed by the Army for use with optical sighting devices. The distance between the small circular eyepieces could be adjusted to accomodate different instruments and head sizes. The filter clips to the head harness behind the user's head, with two hoses drawing air up towards the eyepieces. It was produced in both black and gray (green) rubber. Both of these examples were made by Firestone, in 1940 and 1941 respectively.