Gas was a terrifying weapon but ironically often did not result in the deaths that were feared from it, because it depended so much on ideal weather conditions in order to be effective. But could certainly cause great damage if those conditions were optimal. A first-person account discusses the realities of poison gas and its effects on both horses and men:
“Gas was experienced at Vimy and Ypres, and many casualties occurred amongst our horses, but upon the cases being returned to a place known as Berthenwall Farm, all recovered under the care and treatment of our able Veterinary Staff.
“We had to contend chiefly with two kinds of gas, chlorine and mustard. The former was sent over in cloud form and in shells only. For the cloud gas we were warned from the front line by telephone, so that those in the rear transport lines could prepare for eventualities. Those men and animals caught in the immediate vicinity of the direct forward areas took to the high ground, other transports in ruins of towns made hurried exits, as the latter held gas clouds for long periods."1 [Chlorine gas is heavier than air and collected in low lying areas, and could persist for long periods in places with little ventilation.]
Poison gas was the most feared weapon in the war, damaging men and animals alike. The Medicine in World War 1 page has detailed information on gas types, toxicity, and casualty statistics. Some of that information is repeated here, plus specifics about the impact of gas on horses and mules.
“First introduced on April 22, 1915, the use of poison gas quickly became commonplace by all of the combatants. In the popular imagination, poison gas became one of the defining symbols of the Great War. All of the European powers had signed the Hague Declaration in 1899, never to use poison gas in artillery shells or other projectiles. Again, the Hague Convention of 1907 forbade the use of poison weapons. But once Germany used gas on the battlefield, all other armies began to use it. By 1917, one-third of all artillery shells contained gas. Not surprisingly, then, about one-third of all casualties in the AEF were from gas.”
Treatment of both men and animals was limited to supportive care. Rest and good food brought about healing in quite a number of cases. With mustard gas, immediate washing of the skin and eyes was necessary to stop damage from progressing. Many horses lost the sight of one eye but were able to keep working after recovery. Of course, if the animal was blind in both eyes it would be put down or, if sound enough otherwise, might be sold for meat.
The army responded to this new threat with the formation of what eventually became the Chemical Corps. Research on gas masks was undertaken by all combatant nations, and this included masks for animals.
Tamblyn commented on the use of gas masks:
“The use of gas masks was not practical, more especially under shell fire. Men were instructed to adjust their own masks and bring their animals to safety at a slow trot. Such advice was responsible for the saving of the lives of many men and animals, because, prior to these instructions being issued, a great number of men and animals were killed and wounded in the attempt to adjust gas masks on animals during a gas attack.”3
Mustard gas required different tactics. It was extremely caustic and the least exposure caused blistering of the skin. If inhaled, it was usually fatal, as it caused major injury to the lungs. Gas masks were effective in protecting humans but damage to the skin still resulted because the gas could soak into clothing. For horses, the gas would of course come into immediate contact with their skin and so the only protection for them was to move them away from the area that was targeted. Mustard gas was delivered in shells from long-range guns, targeted using observation aircraft.
When shells bearing gas attacks were observed heading toward picket lines, “the animals were cut loose and driven from the shelled areas, and when Fritz had decided he had done all the damage that could be done, the shelling would cease. The animals would then be returned to their lines, providing, of course, no shells had dropped within the actual lines, as contact with the ground where a mustard gas shell had exploded would be serious for any animal. The least touch of mustard gas on the body of an animal would produce a blister, which, when severe, let to sloughing of the skin.” 4
MAJ Robert D. Walk, a U.S. Army chemical weapons specialist, has written a summary of horse gas masks. He notes,
“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 principal 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. “6
The high breathing resistance of the British mask was a major limiting factor in its use; when Tamblyn is writing about his experiences the mask he had access to was the British mask, which is why the tactics called for moving at a slow trot or driving the animals away from the gas without using masks at all.
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. 7