The Germans were the first to employ deadly gas as a mass weapon of war – most notoriously at the second battle of Ypres in April 1915, where a chlorine attack caused panic-stricken French and Algerian troops to flee in disarray.
The Allies were quick to condemn the Germans but that didn’t stop them retaliating with gas attacks of their own. The British, for example, released chlorine gas at the battle of Loos in September 1915 (only for much of it to blow back towards friendly troops when the wind changed).
We’ll never know for sure how many soldiers died in such attacks, but one estimate puts it at just under 90,000 – with 50,000 of them being Russian. Interestingly, the vast majority of these occurred in 1915.
Later in the war, as armies started employing protective equipment such as filter respirators, deaths from this most infamous of weapons became relatively rare.