Getting PoWs to work on sensitive installations such as railways has always struck me as a brave thing to do. Was there any sabotage that you were aware of?
The French Resistance had some clever methods. Destructive techniques such as mixing carborundum grinding paste with grease for axle boxes (I understand that smearing Vaseline missed with grinding paste over speed camera lenses can have a similarly 'interesting' effect when someone tries to wipe it clean...but please don't try it!) were obvious, but the best were non-destructive techniques which the occupiers didn't discover until too late. For example, with typical Teutonic efficiency, all German railway trucks had a manifest and destination notice secured under a wire panel on the outside of the truck. Swapping a few of those around would mean that urgently needed supplies would be sent hundreds of miles in the wrong direction...and it would take a huge number of clerks days to sort out the resulting chaos
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