[kevinsue]

Originally Posted by gap

Interesting question. Pantelleria never was a submarine base, so Vecko was right in removing it, along with many other harbors, from the list of Mediterranean ports that we can refit from.
Cagliari (Sardinia), Naples (Campania), Messina and Augusta (Sicily) and Leros (South Aegean, Greece), were Reggia Marina submarine bases though. Out of them, due to its position (at the center of the Mediterranean, at the intersection between the Tyrrhenian and the Ionian Sea, and about equidinstant from the Italian bases of La Spezia and Pola), Messina, though officially not being an U-boat base, was of key importance to the German war effort in the Mediterranean, especially in the first year (from '43 on, after Operation Torch and the Allied invasion of North Africa, Sicily became unsafe as it came into the range of Allied air raids).
Matter-of-factly, from December '41 to December '42, there are at least 22 recorded U-boat visits in Messina:

Hello gap, yes it would be handy to have a base at Messina. Even though the base at Salamis isn't included on the SH5 map, the port of Piraeus supports refitting in game. Not sure if a u boat pen is required to be able to resupply at a particular port but the places that appear to support resupply also have a "Radio Antenna" icon on the map.