It was the Germans in WW1 who first realised how chemical weapons could be used to break through a trench stalemate at Ypres in April 1915. It was British gas masks then which nullified this weapon.

The first world war saw the first widespread combat use of modern chemical weapons, starting with the 168 tonnes of chlorine released by the Germans over the trenches near Ypres. Officers hoped ...

In the early days of the air war, chemical weapons detection alarms and tests by U.S., Czech, French and British troops indicated the possible presence of nerve agents and other chemical weapons.

Asaad al-Shibani asks for the support of the global chemical weapons watchdog to "end to ... The state department says Moscow has used a World War One-era weapon to "dislodge" Ukrainian troops.