Mmm...
The Spanish civil war start from 1936 to 1939, and i dont know if a few germans subs were operational (maybe Type II).
It was a war between the Republic and the nacionalists, the nacionalist (leading by Franco) won the war (they had the new BF-190 fighters and Panzers II/III and the Republic had I-16 Polikarpov fighters and T-26 tanks....but in less quantity) and created a fascist regimen that sympathetic with the Nazi regimen.
Hitler and Franco had a reunion with clear intentions: allying Spain with the Axis. Franco wants Gibraltar and more possesions to enter Spain to the Axis powers(Spain was very worn for the Civil War) and, for granted, enter in the Second World War. Hitler can't accept the demands and Spain remained neutral (but Franco Help Germany (secretly) sending the "Legion Condor" and Mölders pilots to the East front (Russia), only for few time)
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It would be interesting see an "alternate history campaign" for Spain in the Second World War, because it's my country.