Peter Falk in his 2006 auto-biography 'Just One Thing: Stories of My Life' states that he didn't like the script for this movie which he thought was hackneyed and full of cliché. Falk wanted to leave the film for these reasons. However, producer Dino De Laurentiis encouraged Falk 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.
Italian censorship visa # 51479 delivered on 26-4-1968.
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 .
The meaning and relevance of this movie's title "Anzio" refers to the Battle of Anzio on 22 January 22 1944 during the Italian Campaign of the Second World War. The Battle of Anzio was an amphibious assault against the Axis allies of Germany and Italy in the Italian regions of Nettuno and Anzio. The name of the World War II military mission that resulted in this combat was Operation Shingle. This operation was aimed at outflanking the German army on the Winter Line and as such allow for an assault on the capital city of Rome, Italy. Operation Shingle was lead by Major General John P. Lucas
The Rapido River was the site of a major assault by the US 36th Infantry (Texas) Division. The attack was repulsed by the Germans with many casualties (143 killed, 663 wounded and 875 missing) The 36th Division was destroyed as a combat capable unit.