Chlorine gas.
Chlorine, a greenish gas, also known as green gas.
This gas, first synthesized in 1774 on modern Earth by the Swedish chemist Scheler using soft manganese ore and concentrated hydrochloric acid, was initially not found to be particularly useful.
However, during World War I, it showed its terror when the German military first used it in warfare.
The time was 5 p.m. on April 22, 1915.
The location, the Ypres area in western Belgium.
The combatants, the German army, and the Anglo-French Alliance.
At that time, the king of the land, the tank, had not yet been invented; the battlegrounds were filled with machine guns, barbed wire, and trenches, and neither side dared to initiate an offensive, as doing so would lead to heavy losses.
The war was at a stalemate until the German army decided to use their secret weapon.
