OSS 117 (1963) André Hunebelle

The story of OSS 117 se dechaine follows secret agent Hubert Bonisseur de La Bath AKA OSS 117, as he investigates the recent death of fellow agent Roos who had an unfortunate accident off the shores of Bonifacio, France while scuba diving. Smelling foul play, Hubert flies into the coastal town of Bonifacio, interrogating all who had interacted with his late friend just before his death. His investigations eventually take him to a remote location, where a new submarine detector has been developed on. This new device could tip the fragile peace between warring factions and cast the earth into another world war, so obviously OSS 117 has to put a monkey wrench in their plans. 

This classy effort is as fun as it sounds, provided by some beautiful photography and an interesting and engaging cast.