I'm looking for a movie about some allied soldiers who go behind enemy lines. Along the way they run in to some deserting German soldiers and end up in german uniforms to sneak through German territory.
I think there was a big castle at some point, and at the end they end up fighting on a train. It was most likely made in the 60s or 70s.

It's definitely not Kelly's Heroes or Where Eagles Dare.

Thanks in advance!