The M5-11-7 Assault Gas Mask was made in 1943, around the same time as the M3 by Mine Safety Appliances, intended to be a lightweight gas mask for use by paratroopers and assault troops because the older M1, M2, M3, and M4 Service Masks used combersome hoses that could impede a soldier's movement. It is one of the most sought after mask 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 neroprene rubber M3-10A1-6 Lightweight Service Mask that had the hose chopped off, the hole plugged up, and had the side of the facepiece butchered 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 oronasal cup unlike the M3-10A1-6 Mask it's made with. The mask was issued with an M7 Carrier Bag, which was made of duck canvas, heavily rubberized with black neoprene, which notibly doubled as a floatation device in the waters off 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 distinctive 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.
The M5 was later deemed obsolete and removed from service in 1947, but still used as a special purpose mask during the Korean War.