Train-derailment strategies varied considerably in their effectiveness. The Germans managed to repair the tracks quickly in agricultural areas with level ground, since the salvage of some matériel was a relatively easy proposition in such terrain. But unbolting a connector plate on an outside rail in a mountainous area (given the higher speed of trains going downhill) could result in the derailment of an entire train with considerable amounts of front-ready matériel strewn far down the mountainside. Among the SNCF employees who joined the resistance, a subset were in Resistance-Fer which focused on reporting the movement of German troops to the Allied forces and sabotaging the railways' rolling stock as well as their infrastructure. Following the invasions of Normandy and Provence in 1944, the sabotage of rail transport became much more frequent and effectively prevented some German troop deployments to the front and hindered the subsequent retreat of German occupying forces.