U.S. Army M1 Dust Respirator
The U.S. Army M1 Dust Respirator consisted of a rudimentary filter pad and a button valve. This example was made by Willson in 1942. Here it has been paired with Sun/Wind/Dust Goggles made in 1974.
Similar masks in my collection: U.S. Navy Type 4 Comfo Respirator
Model stamp "DUST RESPIRATOR M1"
Manufacturer and lot stamp "WILLSON LOT 4"