When Hell Broke Loose (1958)

Near the end of the war in Germany, GI Steve Boland, a self-described "sharp-operator", meets a German girl, Ilsa, and they fall in love. Ilsa's brother Karl, whom she has not seen in three years, and his fellow Nazi Ludwig visit Ilsa. Karl proudly informs her that he and Ludwig are "Werewolves", a group of Nazi assassins parachuted behind Allied lines for the purpose of killing Allied High Command officers. She and Steve go to Army Intelligence with their information, where Steve is immediately arrested for being A.W.O.L. Captain Melton of Army G-2 intervenes on Steve's behalf, as G-2 has had a suspicion about the existence of the "Werewolves" but no concrete info before now.