The Panzer tank featured in the climactic battle scene was the same one used on location for Saving Private Ryan.
When the main character is addressing his men the group shot is overlaid and you can see the same soldiers three or four times in the one shot.
The scenes with the officers in the castle had to be remounted months after production ended when it was discovered that the characters were wearing the wrong uniforms. Originally they wore dress apparel, rather than the more accurate camouflage ones. This led to some characters being recast.
The crew were often used as background characters in shots and so spent most of the production dressed as Nazi soldiers.