Empire Strikes The Bulge!
I've seen this film about half a dozen times in the last 30 years, but, I've only just noticed something. The similarities between it and Empire Strikes Back:
1) Just before the Nazis massacre the marines, one soldier says; "I have a bad feeling about this."
2) When Col. Hessler (Robert Shaw) tells the tank driver to "...finish off..." the Sherman tank, and they blow it up, an almost carbon copy of that scene appears in ESB when the AT ATs blow up the rebel shield generator.
3) At the end when Conrad (Hans Christian Blech) is walking home, there is a wide zoom shot from a helicopter, before he takes off his bags. There is also a similar zoom-in shot at the beginning of Empire, when Luke is astride his Tauntaun.
I think George Lucas may well have been inspired by this movie...