Offensive vs Defensive flavors (Fearless Blue)

Hi all. I am having a bit of trouble with the military equipment - I understand we have red and green colored shields, but they all look the same to me!

Heavy artillery - is that for offensive units only? Light artillery is just for defensive units? When I need more ammo for the "artillery" in my garrisons, that is "light artillery" shells I need to buy?

The terminology is mixing me up, as I was envisioning the heavy artillery as being giant fixed pieces like the Atlantic Wall or Maginot Line...

John Gilbert

Green shields indicate offense; red shields indicate defense.
Heavy Artillery is a green shield, so it's offense only.

Offensive military uses offensive ammunition; defensive military uses defensive ammunition (defensive ammunition is cheaper than offensive ammunition).

So, if you are wanting to buy ammunition for defensive artillery (Light Artillery) you would want to buy Light Artillery Shells. If you want to buy ammunition for offensive artillery then you would buy Heavy Artillery Shells.