TYPE: US Army MI-I-5 Optical Gas Mask
ALIASES: Army Artillery Gas Mask, Army Tank Gas Mask
DATE: c. 1941
FREQUENCY: Scarce
USAGE: United States
FUNCTION: Military
LMàG REFERENCE CODE: US-041
NOTES: During the early stages of gas mask development in 1920s, it was apparent that a gas mask for use with optical sighting devices (like scopes and binoculars) was needed. In 1941, the Army designed and standardized the Army MI-I-5 Optical Gas Mask. It was more or less identical to the Navy version (below) but the two do have some significant differences. The distance between the small round eye pieces could be adjusted via a threaded rod, accommodating a wide range of head sizes. The mask’s filter canister was suspended behind the wearer’s neck by means of a metal clip on the filter that was attached to a canvas sleeve sewn onto the head harness. Inhaled air was drawn through a horizontal slit in the filter. Today, the Army MI Optical Gas Mask is among the rarest of the WWII US gas masks. While the Army version was not made in significant numbers, the Navy Diaphragm Optical Gas Mask was manufactured and issued in quantity to soldiers aboard ships

http://www.gasmasks.net/database/usa3/us-041d.htm

Apparently only 207,544 were ever produced
http://www.wood.army.mil/chmds.....s-04-1.pdf