| In the late 1930s, it was
apparent that a gas mask for use with optical sighting
devices (e.g., scopes, binoculars) was needed. The Army
designed and manufactured the Army MI optical mask in
1941. The NDO Mark I was identical to Army MI optical
mask. It was manufactured and issued in a significant
quantity to Sailors aboard ships. The distance between
the small round eyepieces 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 with a metal clip, which was attached to
the back of the head harness. From a series of small
holes along the back of the filter, inhaled air was
drawn through two corrugated rubber tubes and forced
over the eyepieces to help keep them from fogging. It
was outfitted with a carrier bag and belt.
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