There actually was a raid on Tobruk, 13-14 September 1942, including the German-Jewish SIG and fake British POWs. Unlike the outcome in the movie, "Operation Agreement" was a complete failure.
The actual raid was a complete failure. The seaborne troops failed to land in force. The German and Italian forces rallied and the Allied force had to disperse and flee. The British lost several hundred men killed and captured, one cruiser, two destroyers, six motor torpedo boats and dozens of small amphibious craft.
Actor Leo Gordon was also the screenwriter and had spent most of his career playing murderous outlaws, homicidal killers and assorted brutish and psychotic villains. His role here of Sgt. Krug was one of the few times he actually played a good guy.