The successful defense of Bastogne of the 101 airborne division was due to, as dezrtfish said, mobile artillery. So you should take in several priests with spotters to simulate that.
Another reason why it was successfully defended was the German inability to mount a combined offensive from every direction into Bastogne. This as you might know, was a great advantage for the 101st airborne division, for they had great communications, thus they were able to move quickly to the point of attack and defend. I don’t know how you would be able to put that into the game, but its just a thought. :wink: