I'm slowly getting to grips with how supply works, but where do I get ammunition when it runs out? Do I need to be in a depot/city? I seem to be getting regular supplies but not ammo in small settlements etc.
If you look on page 32 of the manual, you will see a table with general supply and ammunition supply broken out by type of depot and city. As candini5 says, in or adjacent for units to gain supply of both types.