When you fill out one side of the Breakthrough doctrine tree all the way to the bottom you can not fill the other tree all the way down.
If you go for the ISU-152 (or whatever the numbers are) first, you can NOT get the IL-2 Sturmovik bombing runs.
It's vice verca if you go for IL-2s first.
I remember reading this in another thread, but the post was off topic for the thread so I decided to make an own thread for the issue.
