Director Pierre Schoendoerffer participated the battle of Dien Bien Phu as an army photographer. Depicted in the movie by his son, Ludovic Schoendoerffer.
Donald Pleasence caught a virus while filming in Vietnam which put a strain on his heart and started the heart trouble which led to his death in 1995.
As the crowd climbs the steps of the Hanoi Opera House, the names of the work which will be played and its composer can be read on the concert poster: Concerto pour violon et orchestre dit de "L'Adieu" de Georges Delerue (Concerto for violin and orchestra know as "Farewell" by Georges Delerue). Georges Delerue actually composed the soundtrack of the film, his last work for the cinema.
Director Pierre Schoendoerffer was an army cinematographer during the battle. Taken prisoner, his life was spared thanks to the intervention of Soviet cinematographer Roman Karmen who was embedded with Vietminh troops. Karmen allegedly got hold of Schoendoerffer's footage, but they never re-surfaced. Karmen's propaganda footage therefore remains the only one documenting the end of the battle.
The artillery lieutenant played by Maxime Leroux who disobeys orders to deny his howitzers and instead uses them in direct fire against the Vietminh is based on a real officer. Paul Brunbrouck led his African gunners and remnants of North African infantry troops against the Vietminh onslaught and heavily blunted it, leading Giap himself to alter his plans.