The unsatisfactory weight and bulk of the M2 Series Army Service Masks led to the development of the M3-10A1-6 Lightweight Service Gas Mask in 1942, weighing only 3.5 pounds vs. around 5 pounds for the M2. It used the molded rubber facepiece from the M2A2 mask with improved position lower strap rivets so as not to require rifle skids, as well as the improvement of an interior anti-fogging nosecup, shorter M3 Hose (or the previous 27-inch MII Hose cut to adaquate length), and an improved, lighter M10 or M10A1 filter canister. The changes and improvements retained the same level of protection to the wearer as the M2 series masks.
The M3 was initially manufactured from Class 'B' Grey Rubber, but due to increasing natural rubber shortages, black Neoprene (Chloroprene, a synthetic rubber) was used. The Neoprene was found to become unusable in cold weather due to hardening of the mask under those conditions while the natural rubber remained flexible even in cold weather. The production issued plaguing the M3 and the demand for a natural rubber mask to be kept in service resulted in the M4-10A1-6 Lightweight Service Mask in 1942.
The M4 Lightweight was nothing more than a direct reconfiguration of existing M2A2 'Heavyweight' Service Masks, which were upgraded to Lightweight Service Mask standards with the addition of an internal oronasal cup, M7 Harness, the shorter M3 Hose, M10/M10A1 Canister, M6 Carrier, and the C3 Waterproofing Kit. The M4 was issued to fill the gap caused by production issues plaguing the neoprene M3 Series Masks. Around 250,000 M4 Series Masks were procured during the war as opposed to the 13 million M3 Masks later produced. This was largely in part due to the limited procurement of M2 Series Service Masks to modify, as many were needed in their original configuration for general issue or special purpose usage.
Around 1944, the M4A1-10A1-6 Mask was introduced, to improve the downfalls of the older M8 Valve assembly. The mask and its components would be no different than a standard M4, however the only difference was the introduction of the upgraded C15 Valve assembly, which was found to work more effectively in colder climates and also better resisted debis accumulation which may lodge open the valve disk. Very few M4A1's were procured during WWII, with the bulk of them being configured postwar. The main way to tell the difference is that postwar M4A1's will have white rubber valve shrouds with textured pull tabs, while the wartime examples will have black shrouds without any pull tab.
Identifying the M3 and M4 Series Lightweight Service Gas Masks Edit
Both the M3 and M4 series Lightweight Service Gas Masks use similar hardware, but have only one or two distinguishing differences. It can be difficult to distinguish the M4 from the M3 series masks due to the near-identical facepiece and sometimes same Class 'B' Rubber. This table lists the components and construction details across the M3 and M4 series variants:
|Color||Grey or Black (Neoprene)||Black (Neoprene)||Grey||Grey|
|Harness Assy||MIIA1 or M7||M7||M7||M7|
|Rifle Skid (3)||No||No||Yes||Yes|
|Outlet valve (4)||M8 assy||C15 assy||M8 assy||C15 assy|
(1) Harness attaches to the M3 and M3A1 masks with a riveted clip, flat against the mask and near the edge. Lowest strap, at the cheek, is attached to a tab at a 45° angle, at the edge of the mask.
(2) Harness attaches to the M4 and M4A1 masks with a riveted clip on pads. The lowest strap is attached horizontally at the cheek, with the clip pad attachment point forward from the edge of the mask. The two straps on each side are held against the mask by a bridge loop.
(3) The rifle skid is a ridge molded into the mask material, intended to prevent entanglement between the mask wearer's rifle and the harness straps.
(4) The M8 outlet valve assembly has an external guard with a concentric circle grill, as used with the M2A2 Training and Service Masks. The C15 outlet valve assembly has a fully-encapsulating rubber 'shroud' cover with bumps on the interior for de-icing the valve.