I've read about it, but never actually seen it happen. Complete collapse of the German line. The pic below shows the complete crushing of what had been a decent German line with 2 units in almost every hex. The German units left are all ZOCed and don't dare run, since they'll flip and become easy meat for the Russians. So they'll stand and die while the Germans race to pull something together. Probably not until Poland. (There's a few speed bumps in Romania, but that's it.)
Of course it took two O-chits and a double move to pull it off!
