Invisible Agent (1942)

Frank Raymond, grandson of the original Invisible Man, still has the old formula but considers it too dangerous to use, even when Axis agents try to get it. But Pearl Harbor brings him to volunteer his own services as an invisible agent in Germany. Though a bit cold (clothes aren't invisible), his adventures are more comedy than thriller (with occasional grim reminders) as he makes fools of Nazi officials and romances a luscious double agent, in search of Hitler's secret plan...