Hi all, another gas mask. This one was developed in the 1930's, but the can was sealed in 1940. As far as I have seen, and can tell from talking to other mask collectors, this is the only sealed one. As you may know, the M1 and M1A1 masks were also sealed in metal tins similar to this. They required large can openers to open, unlike later masks like the M9 which had key systems similar to their respective filters. Exact canister labeling is:
GAS MASK, DIAPHRAGM
MII-VIII-IIIAI
LOT 2629-5 E A
FILLED SEPT - 1940
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About the mask itself: This was the second major step in US development of a "diaphragm" gas mask, the benefits of the concept being clearer vocal communication by the means of a thin membrane through which sound waves could pass through easily. It shows major improvement from the KTM series masks, and we can clearly see all the parts of the M2 facemask to some degree. The exhale valve is still the relatively primitive flapper style, which was later merged with the diaphragm itself into the circular valve found on the M2 facemask.