(germany) <----- that would be incorrect.

• The first evidence of a "gas weapon", excluding chemically created fire shooting weapons (for ancient flamethrowers - whole other topic), dates back to about 250 AD. The Persians would dig tunnels slightly lower than the Romans', put sulfur in underground, controlled fires in order kill the Romans in the tunnels above (as the gas would obviously rise). The burning of sulfur would release sulfur dioxide, a very toxic gas.

• The most concrete evidence, however, of a "gas weapon" is actually by the Korean. Earliest documentation of a very powerful ship is set in the early 15th century. The Koreans constructed the "Turtle ship". They were later extremely successful in wars, most notably the Battle of Sacheon in 1592. On the front of the ship there is a very large dragon head. This served not only as decoration, but also as a deadly weapon. It acted as a fire pit and they would toss sulfur in the fire whenever they had the chance (whenever the wind was blowing toward the enemy (Japanese) ships).

(If you're interested in seeing a very well though-out war machine, type in turtle ship in a search engine and read up on it. Completely sealed off from invaders gaining access to the inside of their boats and those aboard (spiked top), 26 canons set at different ranges, ~130 people on board, chemical weapon, used for about 4 centuries)