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The M4 Lightweight Service Mask was a gas mask used by the United States during World War II. The unsatisfactory weight and bulk of the M2 series masks led to the development of an improved service gas mask. In 1942, the M3 Lightweight Service Gas Mask was standardized, weighing only 3.5 pounds vs. about 5 pounds for the M2. It used the molded rubber facepiece from the M2A2 mask with the addition of an interior anti-fogging nosecup, and an improved, lighter M10A1 filter canister. The changes and improvements retained the same level of protection to the wearer as the M2 series mask. The corrugated hose between the facepiece and the canister was shortened to save materials. The M3 was manufactured from both grey rubber and black Neoprene (synthetic rubber). 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.

In 1944, the M3A1 mask was released featuring an improved outlet valve. Over 13 million of the M3 series masks were produced during World War II. The M3 series remained in use until obsoleted in 1949.

M4 Lightweight Service Gas Mask

In 1942, the M4 Lightweight Mask was standardized to add additional improvements. It had many features in common with the M3 series, including the M2A2 facepiece, internal nosecup, outlet valve, shorter hose and lighter M10A1 canister. The M4 series masks were made of natural rubber in olive drab color. The Army ordered 250,000 of the masks. A modification to the outlet valve resulted in the M4A1 Lightweight Mask in 1945. The mask was obsoleted in 1949.

Identifying the M3 and M4 Series Lightweight Service Gas Masks

Both the M3 and M4 series Lightweight Service Gas Masks use the M2A2 facepiece, but have a shorter hose and a different canister than the M2A2. It can be difficult to distinguish the M3 from the M4 series masks due to the identical facepiece. This table lists the components and construction details across the M3 and M4 series variants:

   M3 M3A1 M4 M4A1
Facepiece M2A2 M2A2 M2A2 M2A2
Color Grey or Black Grey or Black Olive Drab Olive Drab
Harness Assy M11A1 or M7 M7 M7 M7
Harness Attach (1) (1) (2) (2)
Canister M10A1 M10A1 M10A1 M10A1
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 and M2A3 masks. The C15 outlet valve assembly has a flat, smooth external cover.

M6 Gas Mask Carrier

M6 Gas Mask Carrier

The M3 and M4 series of Lightweight Service Gas Masks required a new carrier bag due to the shorter hose length. The M6 bag was used for both the M3 and M4 masks (and others) to hold the mask itself, the canister, plus accessory items such as anti-dimming sets (to prevent fogging of the eye lenses), covers and protective ointment. The bag has interior pockets for accessories and is stenciled with "Army Lightweight Service Mask" on the exterior front, near the bottom. The M6 bag has a top closure that is secured with three LTD fasteners. Like other WW II webbing and bags, the bag color was OD #3 early in the war but changed to the darker OD #7 shade in 1943.

File:M6 carrier.jpg
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