Masks Animals
in Chemical Warfare

By Major Robert D. Walk

Until recently, armies used animals to succeed on the battlefield. Horses were used for transportation, dogs for protection and detection, and birds for communications. At that time, the threat to animals included pestilence and weapons of war. Because animals were essential, armies used armor and other means to protect them as much as possible.

With the introduction of chemical warfare in World War I, soldiers had to protect themselves and their animals in order to survive and fight. Horses, mules, dogs, and pigeons all required protection from the effects of chemical warfare.

Each animal presented different challenges in protection. Horses breathe through their noses, not through their mouths, so the respirator must only cover their nostrils. Horses eyes are not affected by lacrimators (tear agents), so eye protection initially was not required. Dogs breathe through both their nose and mouth so their protection must cover both. Their eyes must be protected from the effects of lacrimators as well. Pigeons are so small that separate respirators are only envisioned in cartoons. Pigeon protection requires encasing the entire bird.

Goats were used extensively to test chemical-agent effects. Therefore, a means to protect goats also was created. This article describes protection devices for horses, mules, dogs, pigeons, and goats.

Horses and Mules

The horse gas mask of World War I consisted of a large bag that fit over the horse’s nose and mouth. The horse bit into a canvas mouthpiece and the mask was held to the horse’s face by an elastic band. A canvas frame attached to the mouthpiece held the mask away from the nose so the horse couldn’t suck the mask into its nose. The carrier, a waterproof case, was strapped to the bridle or halter.

The United States issued two horse gas masks during World War I. One was a British mask (and the American copy) and the other was the American horse gas mask. The principle difference between the two was the material used for the filter. The British mask, noted for its high breathing resistance, was made of two layers of flannelette impregnated with komplexene. The breathing resistance limited its use in horses used to move supplies and equipment around the battlefield. The carrier was a 5- by 14-inch canvas duck bag. The American horse gas mask was made of multilayered cheesecloth impregnated with komplexene (six layers of cheesecloth) and simplexene (eight layers of cheesecloth) and had low breathing resistance. Because the horses disliked the flavor of this mixture, oilcloth was inserted between the mouthpiece and the cheesecloth. The American carrier was a 10- by 14-inch burlap bag. The American Expeditionary Forces used the British horse gas mask until enough American masks were supplied. The British mask was standard throughout the war.

During the war, the Fifth Avenue Uniform Company of New York City manufactured 377,881 horse gas masks of all types. Of this total, 351,270 were shipped overseas before Armistice Day.

 The American horse gas mask (of cheesecloth) was formally designated the MII horse gas mask in 1925. The British flannelette-type mask was designated the MI horse gas mask. These masks served the U.S. Army through the 1920s. The MII mask was further modified and became the MIII horse gas mask. The MIII was essentially an MII with a metal mouthpiece instead of a canvas one, a fitting role to ensure a good fit, and an outlet valve. The MIIIAI deleted the outlet valve. This mask served the U.S. military through the 1930s. Because the horse was vital to the U.S. military in the 1920s and 1930s, continuous tests led to mask improvements. Until the late 1930s, the design was based on the original "bag over the nose" type. In the late 1930s, new ideas using separate filters were tried and improved.

The M4 horse gas mask adopted in 1941 represented a radical departure from previous masks. Chemical agents were no longer destroyed by chemicals on the mask material but were absorbed by two large cylindrical MI canisters carried on the horse’s shoulders. The M1 canister prevented the rifle from being positioned on the horse’s left shoulder, which meant that the M4 mask was intended for working horses. Two hoses carried air from the filters to a T-connection that combined the airflow and sent it to the mask. The M4 mask was made of rubber and completely enclosed the mouth and nose of the animal. It included a rubber mouthpiece for the horse to bite. A mask carrier hung from the pommel of the horse. Few of these masks were manufactured until the need for horses in the Italian campaign created the need to protect packhorses.

The M5 and M4 horse gas masks were identical in all but one aspect--the position of the canisters. On the M5, both canisters hung from the right shoulder of the horse. On the M4, one canister hung from each shoulder. The M5 mask was designed for the Cavalry. The soldier on the horse carried his rifle in the cavalry standard on the horse’s left shoulder. In World War II, 39,159 M4 and M5 horse gas masks were produced.

(Left) M5 horse mask, stored. Both canisters of the M5 are hung from the right shoulder of the horse. On the M4, one canister hung from each shoulder.
(Right) M4 horse mask and goggles with plastic nonfogging lenses, air-
cushion seal, leather straps.

The M4 and M5 horse gas masks survived the war as standard issue. Experience from flying animals over the "hump" in the China-Burma-India Theater in World War II showed that horses needed supplied air to prevent undue physical and nervous strain. Both horses and mules needed the air to prevent damage to themselves, the cargo, and aircraft. In 1950, the Chemical Corps Technical Committee determined that a suitable mask/airline adapter was required. Horses supplied with air during the flight could be used to move equipment immediately after landing. Tests showed that horses need 4.6 liters of air per minute at 15,000 feet and 13.7 liters per minute at 30,000 feet to prevent physical stress.

The M6, adopted in 1951, was the final horse gas mask. This modification of the M4 mask included a brazed-on Air Force bayonet adapter to attach to the aircraft’s oxygen system. This allowed horses to be transported in unpressurized aircraft (usually propeller driven) at high altitudes without injuring or killing them from lack of oxygen as well as to protect them against chemical agents. The mask was adopted as the "Mask, Oxygen and Protective, Horse, M6." Within the next decade, horses and their associated equipment were deleted from the now mechanized and motorized Army.


The dog gas mask of World War I covered the dog’s entire head and consisted of eight layers of chemically treated cheesecloth. It had two cellulose eye lenses to allow the dog to see, ear pockets for the ears, space for the jaws to work, and a wide neckband with straps to tie around the neck. During the war, the Bureau of Mines and the Chemical Warfare Service conducted tests and experiments on the mask. Use by U.S. armed forces was limited. Little or no experimental work was done between the wars.

During World War II, military working dogs were used in the theaters of war. Several experimental dog protective masks were examined. The E12R8 and the E43R3 proved the most successful. The facepiece of the two masks were similar except for the filter attachment. The E12R8 used a filter mounted on the front of the mask. The E43R3 used two Navy-civilian mask canisters mounted on the sides.

Ultimately, the E43R3 was standardized as the M6 dog gas mask. This mask used a reclaimed, coated canvas duck muzzlepiece equipped with one large, glued- in, slightly bulged cellulose acetate eye lens. The M6 fitted over the face and muzzle of the dog. The outlet valve was located directly under the muzzle. It used two M12 (E40R1) filters¾one filter positioned on either side of the mask under the eye lens. A three-strap harness held the mask on the dog’s head. The M8 (E10R1) carrier stored the M6 when not in use. Thus, the mask was known as the Mask, Gas, Dog, M6-12-8. During the war 1,409 were produced.

Military working dogs were still used during the Vietnam War. The dogs needed respiratory protection, but the M6 mask was no longer useful. Dogs procured by the armed forces could not wear the M6 mask. Even if the M6 masks were the correct size and proper fit, only 32 were available and they were in poor condition. New masks were needed. This meant either procure the M6 again (which was not acceptable, because of its small size) or design, develop, test, adopt, and procure a new mask. One requirement for a new dog detection system included respiratory protection, which eliminated the stand-alone dog protective mask program. The M6 dog gas mask was declared obsolete in 1969.


Pigeons used during World War I were protected with the same flannelette material used in the horse gas mask. Gas-proof covers (measuring 15 by 15 by 24 inches) of this material were used to cover the pigeon cages in the event of a gas attack. If no covers were available, the pigeons were released to fly above the gas cloud to escape the effects of the gas. World War I doctrine stated that pigeons could be used during a gas attack because they could quickly escape the gas.

Pigeons also were used for communications during World War II. During the war, 36,000 pigeons were deployed overseas. If chemical warfare were initiated, these pigeons had to be protected. Three protectors were used. The M1 pigeon protective bag was large enough to contain a small pigeon cage, and it had a hose leading to an accordion-styled air pump with a filter canister attached. The M2, measuring 65 by 22 by 14 inches, had a large acetate window on the side and held a large pigeon cage. The M3 held a smaller cage and had a window on either end. The M2 and M3 bags used a bellows attached to an M1 training filter to supply air to the pigeon. Of these masks, only the M2 survived the immediate aftermath of the war as standard issue.

Pigeon cages were made a standard size in the post- war years. These new cages made the M2 pigeon protective bag impossible to use, and it was declared obsolete in 1948. The E7 Pigeon Protective Bag was designed using the standard pigeon containers PG-103/CB, PG-105/CB, and PG-107/CB as models. During the next five years, various revisions of the basic design resulted in a lightweight, durable 12 ¼- by 14 ½- by 9-inch bag with carrying straps and a tube leading to a bellows unit with an attached M11 filter canister. The handler pumped the bellows for five minutes every four hours to force clean air into the protector. The larger pigeon crates PG-49 (12 birds) and PG-50 (20 birds) required a larger protective bag. This bag, the E8, opened to 33 by 19 by 9 inches to accommodate the larger pigeon crates. Despite the unexplained nonconcurrence of the Signal Corps representative, these bags were adopted in 1951 as the M4 (former E7R2) and M5 (former E8R2). Pigeons and their associated equipment were deleted from the inventory within the next decade.


While not used extensively in war, the United States used goats to test chemical-agent effects. In 1945, the United States developed the goat gas mask. Although never formally adopted, the mask was designated the E46. It used the Army standard M10A1 filter and was stored in the E12 carrier. At least 25 were produced to use in agent testing. The goat gas mask lives in the minds of most chemical soldiers because several 1950’s vintage Army training films show goats exposed to nerve agents. Tethered beside each other, one goat is protected and one is not. The cannons fire, the agent cloud rolls over the goats, and the goats are exposed to lethal concentrations of nerve agents. The unprotected goat dies horribly from the nerve agent, but the protected goat survives because of its E46 goat gas mask. The cessation of open-air testing of chemical agents using goats ended the need for this mask.


This article examined chemical-protective apparatus for horses, dogs, pigeons, and goats. Any animals used by the military in a chemical war must be protected to ensure their continued survival. Based on need, the U.S. military has always protected its animal workers the same as their human soldiers

MAJ Robert D. Walk is currently assigned to the U.S. Army Reserve Command’s DCSOPS in the Weapons of Mass Destruction Division. He is a graduate of Command and General Staff College and the U.S. Army Chemical School. He is a graduate of the University of New Hampshire with a B.S. degree in Chemical Engineering, an M.B.A. degree from Long Island University, and an M.S. degree in Civil Environmental Engineering from the University of Oklahoma. MAJ Walk can be contacted through the Chemical Doctrine Net.