History books record that the first instance of Germany using poison gas was at the Western front at the second battle of Ypres. This is true — but there were earlier attacks using nonlethal gas. French forces fired grenades filled with xylyl bromide – tear gas – at German lines, hoping to incapacitate them long enough to take over their positions. Germany’s initial field-of-battle experiments began six months later, in the battle of Bolimov, near Warsaw, against the Russians.

On this day, January 31, in 1915, Germany fired the first liquid-gas-filled shells at the Russians. As before, it was only with xylyl bromide. But what worked in the European summer failed in the Russian winter: not only did the liquid carry back to the German lines, but much of it failed to vaporize — unsurprising, given the below-freezing temperatures on the field of battle.

While poison gas killed relatively few soldiers in WW I, its use caused a psychological fear large enough to warrant a convention of the major world powers in the years after the war, to agree on a ban of the use of all chemical weapons in warfare. That convention was largely followed throughout WW II and beyond.