Peter Falk in his 2006 autobiography "Just One More Thing: Stories of My Life" stated that he didn't like the script for this film, finding it hackneyed and full of cliché; he wanted to leave the film for these reasons. However, producer Dino De Laurentiis encouraged him to stay by giving him film-poster name-above-the-title credit as well as choice of writer for his dialogue. Falk stayed on the picture and apparently actually wrote his own dialogue.
After the war, Major General John P. Lucas, who commanded American forces as Anzio, visited war hero Audie Murphy on a movie set. Murphy, who had served at Anzio returned his salute, but refused to shake his hand as he held him responsible for the deaths of many men during the battle.
Based on true events. On January 30, 1944, about a week after the initial landing, two battalions of Rangers did indeed try to infiltrate German lines and take Cisterna. They did in fact walk into a trap. All but a few of the 700-odd men (Earl Holliman's character and Robert Mitchum's character both cite the number '767') involved were killed or captured.
Location filming for this movie was conducted in and around the environs of Rome, Italy.
The "Black Devils" was the nickname of the 1st Special Service Force, The Devil's Brigade (also called The Black Devil's and The Black Devils Brigade), a joint American-Canadian commando unit organized in 1942 .