If got assigned a grid way down there by Spain as well, and i was cutting it really low of fuel for a safe return trip and was out of eel's by the time i had completed the patrol of my grid, so i stopped in at one of the German supply ships that are in a couple of the Spanish ports, they should be marked in on your map in blue, and work the same as docking at any other friendly navel base
Got my tanks topped up with diesel and a full load of eel's and was ready for the return trip! :p