Special Train for Hitler
 

Unlike many mainstream movie spankings which are often quite lighthearted and either last about 10 seconds or are over the girls skirt, this is more serious.

It features a train in the 2nd World War with prisoners whose female SS guards are captured by the resistance fighters. The head guard is taken to one side of the carriage and despite her struggling and protesting, has her white shirt removed, her thick woollen skirt is unzipped and pulled down to below her knees. She's wearing a black bra and brief see-through black panties. The other women look on in horror.

The resistance fighter then swings her across his knees for a real leg-kicking protesting spanking over those skimpy panties. She cries and tries to resist but to no avail. Another of the guards, this time a blonde, tries to make a run for it. But someone goes after her and forces her back down on the bed. She too is undressed but she's not wearing any bra and we presume she gets similar treatment. The action swings back to the original girl who has now been stripped completely. Her spanking continues with good shots of her naked breasts and face as well as her rear.

All in all, 3 minutes of high action

I've seen it and agree that its one of the best scenes ever.

The title was "Train Spécial Pour SS." It was filmed in 1977.