(Taking Port Said at the end of the North Africa campaign cost me more casualties to my armor units than the entire rest of the campaign combined because I could only attack with two units and can't cut supply. I had to change the advancement of my tanks to Heavy Armor to do it, as well.)
I understand why basic supply exists, but if I interdict literally all supply coming to a port, that port shouldn't give even basic supply to its units, just so that blockades can actually have some kind of meaning.
Besieging Oslo, my units were taking efficiency loss because of snow, but thanks to the odd way weather works in Norway, Oslo gets North Atlantic weather (and so do four other hexes in Norway), so the Germans are immune to the weather efficiency loss. This basically means the only thing I can do is keep attacking while my units have priority reinforcement to gradually whittle them down with attrition by pure lack of ability to reinforce their own side because they can never be out of supply, and I can't bring enough forces to overwhelm them.
