The Guns of Navarone — Greece
Allied commando team destroys massive German guns on a fictional Aegean island, allowing the evacuation of 2,000 soldiers.
The Dodecanese islands were a genuine strategic prize — German control of Aegean gun batteries blocked Allied shipping and supply routes to the Eastern Mediterranean. The failed British attempt to seize the Dodecanese in 1943 (Operation Accolade) is the real-world inspiration.