The film recounts the formation, training, and first mission of the 1st Special Service Force, a joint American-Canadian commando unit, known as the Devil's Brigade. The film dramatizes the Brigade's first mission in the Italian Campaign, the task of capturing what had been an impregnable Nazi mountain stronghold, Monte la Difensa.
American Lieutenant Colonel Robert T. Frederick is summoned to Britain where he is authorized by Admiral Louis Mountbatten to raise a commando force comprising both American and Canadian personnel for operations in Norway.
Back in the U.S. Frederick receives his American troops — all are Army convicts. When the Canadian contingent arrives they immediately cause friction with the Americans and chaos ensues. By the time Frederick manages to overcome the national differences and to mould the First Special Service Force into a highly trained commando force, the Allied High Command have had a change of heart and offered the Norway missions to British troops. Left without a role, Frederick manages to persuade Lieutenant General Mark Clark in Italy to give his men a chance to prove themselves.
Clark asks Frederick for the 1st Special Service Force to reconnoiter a German garrison in an Italian town, but Colonel Frederick decides to go one better and capture the entire town. In the process, they earn the nickname "Die Teufelsbrigade" — The Devil's Brigade.
Convinced now of the ability of Frederick's men, General Clark gives them a task no other Allied troops have managed to accomplish — to capture Monte la Difensa. Facing severe obstacles, the Devil's Brigade attacks the undefended eastern side of the mountain by scaling a cliff the Germans believed could not be climbed. Reaching the top as a unit, they take the stronghold despite losses to the Force, allowing the Allies to continue their advance north into Italy.William Holden as Lt. Col./Col. Robert T. Frederick
Cliff Robertson as Maj. Alan Crown
Vince Edwards as Maj. Cliff Bricker
Andrew Prine as Pvt. Theodore Ransom
Jeremy Slate as Sgt. Patrick O'Neill
Claude Akins as Pvt./Cpl. Rockwell W. "Rocky" Rockman
Jack Watson as Cpl./Sgt. Peacock
Richard Jaeckel as Pvt. Omar Greco
Bill Fletcher as Pvt. Billy 'Bronc' Guthrie
Richard Dawson as Pvt./Cpl. Hugh MacDonald
Tom Troupe as Pvt. Al Manella
Luke Askew as Pvt. Hubert Hixon
Jean-Paul Vignon as Pvt. Henri Laurent
Tom Stern as Capt. Cardwell, Garrison CO of Fort William Henry Harrison
Harry Carey Jr. as Capt. Rose
Michael Rennie as Lt. Gen. Mark W. Clark, Commander of the U.S. Fifth Army
Carroll O'Connor as Maj. Gen. Maxwell Hunter
Dana Andrews as Brig. Gen. Walter Naylor
Gretchen Wyler as the Lady of Joy
Patric Knowles as Adm Lord Mountbatten
Wilhelm Von Homburg as Fritz
James Craig as Maj. Gen. Knapp
Richard Simmons as Gen. Bixby
Norman Alden as the M.P. Lieutenant
Wolper had purchased the film rights to Adleman and Walton's book, but found that no film studio would back him. The motion picture was filmed with the 19th Special Forces Group at Camp Williams, Utah, 20 miles south of Salt Lake City, with battle locations on Mount Jordan — just above Draper, Utah — and on location in Santa Elia Fiume Rapido, Italy. David L. Wolper realised it would be as cheap to shoot in an Italian village as building an Italian set in America. However, the birthday scene which appears to be in Italy was filmed at the National Guard Armory in Salt Lake, with Brigham Young University students as extras. This was a bit of a problem because the party scene required the "soldiers" to be drinking and smoking and BYU students don't. Smoke generators had to be used on that set as well as on the battle field. That was a time of civil unrest, and black activists complained about no black actors being in the film. There were no black actors hired because there were none in the unit. The U.S. Department of Defense provided 300 members of the Utah National Guard to play soldiers in the mass battle scenes filmed.
Wolper had the Brigade wear attractive but fictional red berets that appeared as well as on the film's posters and on the tie-in paperback cover of Adelman and Walton's book. At the end of the credits the copyright date reads MCMXLVIII, which is the Roman numeral rendition of 1948; the year of production of this film was actually 1968 (MCMLXVIII). During the film a map of Europe appears twice in Colonel Frederick's office, showing Europe after the war with West and East Germany and Poland with its post-World War II borders.
The cast of The Devil's Brigade included NFL running back Paul Hornung and World Middleweight Champion boxer Gene Fullmer in minor roles. They can be seen in the barroom brawl sequence, Hornung as a belligerent lumberjack and Fullmer as the bartender.
Alex North composed the soundtrack of the film, re-purposing the theme from his rejected score to the pilot episode of The Rat Patrol. At the time of release only a cover version of the soundtrack album by Leroy Holmes was released by United Artists Records. The album was illustrated with the original Sandy Kossin artwork of the film and featured instrumental (with whistling) and a male chorus singing lyrics to North's title theme. The album also contained cover versions of other North themes from the film as well as 1940s popular music that appeared in the film.
In 2007 Film Score Monthly and Intrada released a limited CD edition of North's original soundtrack with Kossin's artwork including alternate versions of the title theme, North's own arrangements of four 1940s jazz popular tunes, two traditional Christmas carols, and the pipe band version of Scotland the Brave featuring in the film.
The pipes and drums featured in the production were the "Salt Lake Scots Pipe Band" who furnished their own instruments and uniforms for the film shoot. The band still exists today.
The film was the 4th most popular movie in general release in Britain in 1968, after The Jungle Book, Barbarella and Carry on Doctor.
To the veterans of the Force, the film was historically inaccurate. In a T.V. documentary Suicide Missions: The Black Devils, Force member Bill Story stated:"The Devil's Brigade was and is a very entertaining war movie. But as a piece of accurate history it's sheer nonsense. There was never an aspect of The Dirty Dozen. This was absolutely not true."