This is a bug I encountered about a day ago. Here we can see that my Squadron Commander has gained the Field Commission promote, and a description of how it works:
And here's a picture of a Trench Fighter packed into that same Squadron Commander, outside of friendly territory, with their Upgrade action disabled. As it turns out, the Trench Fighter cannot be upgraded because it must be in friendly territory, despite what Field Commission claims to allow:
(There's a chance I may be choosing promotions sub-optimally but let's leave that alone for now)
And here's a picture of a Trench Fighter packed into that same Squadron Commander, outside of friendly territory, with their Upgrade action disabled. As it turns out, the Trench Fighter cannot be upgraded because it must be in friendly territory, despite what Field Commission claims to allow:
(There's a chance I may be choosing promotions sub-optimally but let's leave that alone for now)
