Black Dragons (1942)

If this isn't a piece of propaganda, then I shall never know what it. A secret Japanese society (think Yakuza meets Fu Manchu) gets the Nazis to send an evil doctor to substitute some important American industrialists whose future role will be to sabotage arms production plants during the war (that we didn't know we were going to have yet...!). Those devious Japanese, though, double-cross "Dr. Melcher" (Bela Lugosi) and imprison him so he cannot divulge the secret identities to anyone. Needless to say, he escapes and exacts revenge of the fifth columnists. The deaths of such high profile citizens naturally engage the attention of the FBI - and it's a race against time. It'd make a hell of a lot more sense if you saw the last ten minutes first; as the piecing together of this tale takes quite a bit of cerebral effort - not sure it was quite worth it.