@Dylan:
Units
Poison Infantry
Poison Infantry are strong Infantry that are upgraded Infantry
If you want upgraded infantry in your game, you might want to simply call them Upgraded Infantry or Elite Infantry, two terms that would be immediately understandable. It would be a better choice than “Poison Infantry”, a term that as far as I know never existed. Poison gas was definitely used in WWI, but it was simply released against enemy lines under favourable wind conditions and followed up by a conventional attack. Attacking troops might have worn gas masks if they attacked before the gas had cleared, but this would not have made them special infantry (any more than the gas masks worn by the defending troops would have made them special). The best example of true WWI elite troops that I can think of were the Stormtrooper units (“Stosstrupen”) used by Germany towards the end of the war. They were specially trained to use infiltration tactics, a method of attack which was arguably the most effective way for troops to deal with the trench environment of WWI. These tactics were the forerunner of the way in which modern infantry operates. The British also started using infiltration tactics towards the end of the way (though without the catchy Star Wars-like name for their infantry), so I don’t think there would be a historical problem with each side in your game having a category of Elite Infantry.