The M5-11-7 Assault Gas Mask was made in 1943, around the same time as the M3 by Mine Safety Appliances. It was intended to be a lightweight gas mask for use by paratroopers and assault troops. This was because the older M1, M2, M3, and M4 Service Masks used cumbersome hoses that could impede a soldier's movement. It is one of the most sought after masks by collectors due to its usage in the Normandy landings in 1944.The M5 was based on the British Lightweight Service Respirator, featuring an filter input on the side of the mask. The mask is made of a neoprene rubber, the M5 facepiece was a separate fabricated model made with it's own mold to the M3 service masks, and are not re-issued facepieces. The facepiece altered to fit a 60mm threaded inlet valve for the filter. Another variant was made of an M2A2 or M2A3 Heavyweight Service Mask in the same way.
The mask did not feature an oral nasal cup like the M3-10A1-6 Mask, The mask was issued with an M7 Carrier Bag, which was made from duck canvas that was heavily rubberized with black neoprene, that notably doubled as a flotation device in the waters of Normandy, as well as an M11 type filter (which was also issued with the M8 Snout and the M9 masks). The M5, as well as all the other gas masks made of neoprene had one distinct problem - the facepiece hardens during colder weather, a condition known as "cold set".
An attempt to replace this mask was made with the M8 Snout-Type Gas Mask , which was made from an M3, M3A1, M4, or M4A1 Lightweight Service Mask facepice (made of Class "B" Grey Rubber) that had the hose removed and an angle pipe fitted with a 60mm threaded inlet valve fitted in place of it.