Guns of Navarone ratings (Movie franchise)

Plot of the first movie: Two powerful German guns control the seas past the Greek island of Navarone making the evacuation of endangered British troops on a neighboring island impossible. Air attack is useless so a team of six Allied and Greek soldiers is put ashore to meet up with partisans to try and dynamite the guns. The mission is perilous enough anyway, but are the Germans on the island getting further help too?