I just made the first chlorine gas attack (as Russia btw) and it all sounded rather simple but in the end I was left with more questions that before.
I used the event on a neighboring province (Lemberg) which I did not have troops in and then moved a stack in to attack.
What happened was that the enemy stack moved out without apparent losses. It was of course destroyed in later turns but not what I had hoped for with the first use of gas which was practically without effect.
What is the best way to use it, the first attack especially? Does it have to be on a region that is already under siege or can I put it in neighboring regions too?