Donald Pleasence, Nigel Stock and Gordon Jackson all star as German soldiers in this film, which was shot just a few years after The Great Escape in which the same three played British prisoners plotting to escape from a German POW camp.

The character of General Tanz was influenced by the career and reputation of real-life Panzer (tank) officer Col. Joachim Peiper, the youngest man in the SS to be make the rank of full colonel (SS-Standartenführer, the direct SS equivalent to an Oberst or full colonel in the German army). Peiper - a protégé of Reichsführer-SS Heinrich Himmler, the head of the Schutzstaffel (SS) and the second most powerful man in Germany after Adolf Hitler - was promoted to the rank at the age of 29. It was Peiper's unit of the Waffen-SS, Kampfgruppe Peiper of the 1st SS Division, Leibstandarte SS Adolf Hitler (German for "Adolf Hitler's Bodyguard Regiment"), that was responsible for the Malmedy massacre of captured American soldiers depicted in the earlier film Battle of the Bulge (where a character directly based on Peiper was played by Robert Shaw). After the war, Peiper was convicted of war crimes and sentenced to death. The sentence was commuted by American occupation authorities, as the trial had been fraught with illegalities, and he served only 11 years in prison, despite having perpetrated war crimes on both the Eastern and Western fro

The film was one of the last to run into heavy censorship trouble before the abolition of the Production Code Administration and its replacement with the voluntary ratings system (G through X) by the Motion Picture Association of America (MPAA) in 1968. According to former PCA Director Geoffrey Shurlock, this film was troublesome due to its depictions of sexual behavior, which the producers tried to get away with by using silhouettes and shadows.

Valentine Dyall dubbed a number of small part players.

The same year that this film was released, Charles Gray and Donald Pleasence both appeared in the James Bond movie You Only Live Twice. In it, Pleasence played Ernst Stavro Blofeld, a role that Grey would later play in Diamonds Are Forever.