Rare photographs of war dogs with gas masks, 1915-1970

There was nothing more terrifying than the call for a gas attack in the trenches - "Gas! Gas!". This warning call sent men scrambling for their masks as a poisonous fog engulfed them.

For years, soldiers succumbed to the strangulation effects of chlorine, phosgene, and mustard gas as motionless armies found new ways to defeat each other. And it was not only human combatants who suffered – many military work animals were killed by chemical weapons.

Dogs have been used in warfare since ancient times, serving as sentries, messengers, attackers and even mascots. About one million dogs were killed in action in World War I, a conflict that also saw the first large-scale use of chemical weapons. The destructive effects of these gases spurred the development of masks to be worn to counter those agents.

After the first use of poison gas by German forces in April 1915, the British and American governments quickly sent a series of masks designed to filter the toxic gases and keep their soldiers alive. Due to the important combat role played by dogs at the time, they also developed the canine gas mask.

The Germans used about 30,000 dogs on the Western Front, and the Entente kept about 20,000. Some dogs pulled heavy machine guns on trolleys, others used their keen sense of smell and hearing for sentry and scout work. Their small size helped them to slip further between trenches for conveying, shuttle medical supplies, or lay communication cables.

In a less formal way, dogs improved morale within the trenches by hunting rats and acting as companions to soldiers in miserable conditions. Here is a collection of photographs of war dogs wearing gas masks against the threat of chemical warfare.