The film starred Robert Mitchum, Peter Falk, and a variety of international film stars. The all-star cast mostly portrayed fictitious characters based on actual participants in the battle. The one exception was Wolfgang Preiss, who played Field Marshall Albert Kesselring. This was a U.S./Italian co-production made in Italy with an Italian film crew; however, none of the major stars were Italian, nor were there any major Italian characters.
Ennis is with the Rangers when they are ambushed at the Battle of Cisterna. From there, the film departs from being a view of all sides and levels of the campaign to a story of a handful of survivors making their way back through enemy lines. During the film, Ennis seeks an answer to the question of what makes one human being willingly kill another. Corporal Jack Rabinoff (Peter Falk) replies that he loves it, and his lifestyle makes him live more than anyone else. Rabinoff is based on a real First Special Service Force soldier Jake Wallenstein, who ran an illegal brothel of Italian prostitutes in a stolen ambulance. Most of the men, including Rabinoff, are killed. In reality, Rabinoff was killed by shrapnel at Port Cros during Operation Dragoon, the invasion of Southern France. Ennis survives to publicly question the competence of the Allied commander.
Peter Falk thought that the script he read was cliched and wanted off the film. At the last minute Dino DeLaurentiis allowed Falk name above the title billing and the writer of his choice to do his characters dialogue, Falk stayed on the film and wrote his dialogue himself.