Offensive chemical troops generally date back to WW1 and have in time included a lot of "non-conventional" weapons outside outright WMDs, i.e. pretty much anything that doesn't fire solid shells.
As far as I have understood Russian/Soviet doctrine on this, all flame weapons are managed by chemical units (generally at division level even now) and get task-allocated to battalions as needed. Includes everything from flamethrowers to modern TOS MRL.
This sounds strange now that I think about it, since it means that you have to have specialized personnel to fire even a disposable RPO-Z, while e.g. the US M-202 could be (doctrinally) handed over to squad-level AT specialists instead of the Dragon. Oh well.
For reference, smoke generators are also still handled by "chemical" units in the US Army. So there
