They're M-47s. At least the "toy" Col. Hessler made the comment "Germans are still the best toy makers in the World!" about was modeled after the full-size props.

At least they painted them grey and put German crosses on them.

In any event, I still enjoy that movie but I make a mental note while watching it to not compare it to the actual events in The Battle of the Ardennes/Battle of the Bulge. It is far too inaccurate to be taken as a serious retelling of the BOTB.