From: Bristol, UK
And be careful setting all depots in Sicily (or anywhere) to 4. It's OK if you don't have too many, but as Loki said the limit is ports. If you are using all the port/shipping capacity, setting further depots to 4 does not increase the total flow, it just hits all the depots with something like 'equal hurt' (actually worse, it will supply the nearer ones to ports better I think and starve the forward ones). In other words they all get slowly strangled. Set the key 2-3 at level 4, and the rest at 3. When you invade italy, you will need Sicily to drop supply demand (even if you have a/c based there - that shipping again). Even disband inland ones, and just sit refitting units in ports.
I have a cunning plan, My Lord