Okay, definately hollywood version of the battle. My neighbor across the street was near there for the Battle of the Bulge. Messier, colder, and less considerate. This could probably use a remake. Overall, a good story, but I didn't really feel deeply enough for the characters, and the ones I did feel for, they survived. As a War film for its time, I'd give it 7 out of 10 stars. I'd probably drop a star or two modernly as it would not really hold up.
And yes, there really was a bunch of Nazi infiltrators who dressed up in American uniforms/equipment and spoke english, and did alot of damage. They were Otto Skorzeny's Grief Commandos from the SS Panzer Brigade 150 and were officially named Einheit Stielau. Of the 2500 that were to break into allied territory, only 44 managed to do so and 18 were captured and shot as spies.