GERMANY
Chlorine was used by Germany in the second battle of Ypres. In THE LATE AFTERNOON OF April 22, 1915, members of a special unit of the German Army opened the valves on more than 6000 steel cylinders arrayed in trenches along their defensive perimeter at Ypres, Belgium. Within 10 minutes, 160 tons of chlorine gas drifted over the opposing French trenches, engulfing all those downwind.