Artistic License - Military: The "sturmbanführer" who speaks with the Tiger tank commander actually has the insignia of an untersturmführer (lieutenant).
Author's Saving Throw: Oddball's "pipe on the gun" claim covers the fact that the Shermans used for the movie had been up-gunned postwar.
Executive Meddling - According to Clint Eastwood, MGM, against both his wishes and those of director Brian G. Hutton, re-edited the film to remove some character-driven scenes and a more obvious anti-war message. This was also responsible for the addition of "Burning Bridges" as the title song, rather than the original theme composed by Lalo Shifrin.
Genius Bonus: Moriarty describing the "captured" Tiger as a "piece of junk" with "fuel leaking everywhere". Deadly as they could be Tiger tanks were also underpowered, mechanically unreliable and notoriously leaky since wartime shortages meant their fiendishly complicated fuel systems (5 tanks and over 120 tubes and fittings) were made with household plumbing pipes instead of military grade materials
One of the assistants working on the film was a young budding filmmaker named John Landis. While in Yugoslavia shooting the movie, Landis witnessed an event involving gypsies burying a corpse in the middle of a road which inspired him to write the script for An American Werewolf in London. He also got to be friendly with one of the Kelly's Heroes stars, Donald Sutherland and years later got him to an appear in two of his early films, The Kentucky Fried Movie and Animal House.
During the filming in Yugoslavia in July 1969, Neil Armstrong became the first man to walk on the moon.
This film is an obvious favorite of the makers of Girls und Panzer, including one character calling herself "Sargent Oddball" as a hasty alias, and one team of girls watching the movie for inspiration the night before the national finals. Said team invokes "Operation Kelly's Heroes" in said final battle.