"But a German scientist came forth with a scheme for breaking the dead-lock [in World War I trench warfare]. This was Professor Nernst, the inventor of a well-known electric lamp and a man who had always violently hated the British. His plan was to drown out the British with a flood of poisonous gas. To be sure, there was the pledge taken at The Hague Conference, but why should that stand in Germany's way?'" - Inventions of the Great War, Bond, 1919
Well, technically it said "Prohibition of the Use of Projectiles with the Sole Object to Spread Asphyxiating Poisonous Gases." Wafting the gas over was OK in the German mind. Although this kind of stuff didn't make it hard for the allies to paint Germans as evil. And in WWII, they continued to dig that hole deeper.
'On one occasion in 1916 a cloud of gas was released upon an Irish regiment. The wind was rather fickle. It carried the gas toward the British trenches, but before reaching them the cloud hesitated, the wind veered around, and soon the gas began to pour back upon the German lines. The Germans were entirely unprepared for this boomerang attack. Many of the Huns had no gas-masks on, and those who had, found that the masks were not in proper working-order. As a result of this whim of the winds, eleven thousand Germans were killed.' -- Bond, 1919