Chemical weapons have dominated the headlines recently — two Russians were exposed to the Novichok nerve agent in the UK, sparking an international incident; the airstrikes in Syria were spawned from reports of a chemical attack on civilians. In Douma, Syria, the specifics aren’t exactly known about the agents used, but most sources say it was some sort of combination of chlorine and an unknown nerve agent, though sarin has been used in Syria in the past — in April, 2017 and August, 2013. The Organisation for the Prohibition of Chemical Weapons (OPCW) has been granted access and is conducting an investigation in Douma right now.

The use of chlorine in chemical warfare dates all the way back to World War One. Typically delivered by artillery shells, the heavy gas proved to be both particularly useful and devastating as it was heavier than air — in trench warfare, there would be no escape from the gas as it permeated low-lying areas. Moreover, enemy troops didn’t need to breathe a whole lot of it to take them out of the fight, unlike other forms of gas that had been tested. The soldiers would report the smell of pineapple and pepper as the yellow-green gas crept for them in their trenches, and then it would be too late.

It was first used by the Germans on April 22, 1915. It was the Second Battle of Ypres, and the surprise use of chlorine gas was extremely effective, wiping out two Algerian and French divisions. It was so effective, that the Germans hadn’t planned on what to do with that big of a hole in the enemy lines. The Allies quickly made do and kept the Germans at bay.

The other countries soon fell in suit — the British used it in September of that same year. The Australians did the same in June, 1916. By the end of the war over 90,000 troops had been killed by gas (not necessarily chlorine), and over one million were wounded.