On second thought...I'm willing to bet money that nobody will guess this film.
It's an obscure British movie called Went the Day Well. If it's remembered at all today, it's because its story of German paratroopers invading England in disguise inspired The Eagle Has Landed. I use it in my War & Society in 20th-Century Britain class, along with Mrs Miniver, which is why it popped into my head.
So, here: this one should be much easier.
