Flares: I think these were the Rail Union (Cheminots). They had flares and also had some sort of big boom-machine: they would make a very loud explosion with it every 100 feet or so.
Flares:

I think these were the Rail Union (Cheminots). They had flares and also had some sort of big boom-machine: they would make a very loud explosion with it every 100 feet or so.