Here's a little something I've had kicking around for a while now and keep meaning to add to the forum. The mask came with a whole load of other stuff that I bought trade from the good old U.S. of A. When I noticed this in the parcel I thought that it was worth keeping for my own collection.
The mask itself is the second type or version of the U.S. M1-1-5 Optical Gas Mask, being nether an Army nor Navy item, and is in fact a hybrid of components used by both services. The face piece is the Army version in back rubber, with navy style filter canister and harness. Apparently designed to be used primarily by the Navy, however due to supply out stripping demand, ended up being used by both services. The M1-1-5 Optical Gas Mask was only ever made in very limited numbers, with production figures ranging from 1000 - 3000 units produced annually, due to its specific designated use, by service personal who required the need to use optical equipment during a gas attack. Troop and servicemen such as Artillery officers, Snipers and Ships Captains etc, would carry this type of mask and its latter versions instead of the standard Army or Navy equivalent. The M1-1-5 Optical Gas Mask series was soon superseded by the NDO 1 (Navy Diaphragm Optical, USN Marked face piece) and the U.S. Army M2-10-6 Lightweight Optical Gas Mask.
My Mask came complete with its bag and anti-dim kit, and was manufactured in late 1943 by (MSA) Mine Safety Appliance of Pittsburgh, who also made a large range of civilian and military respiratory equipment during both world wars, and are in fact still in business to this very day.
Remember some WWII gas masks can contain blue asbestos so should never be worn.