Gustav beiler, a British secret agent stationed at Saint-Quintin, a French city eighty miles south of the English Channel, was on the run from the Gestapo. But he refused to allow that peril to prevent him from carrying out the crucial mission that had been assigned to him in London: orchestrating a sabotage campaign by railway workers to destroy the French network that Feldmarschall Erwin Rommel would be counting on to rush reinforcements to Normandy when Allied forces invaded. It was mid February 1944. Aided by detailed information provided by the Railway Research Service (RRS), a secret operation in England, Beiler was able to pinpoint critical facilities in northern France’s rail yards: tracks, repair shops, sidings, stations, roundhouse, turntables, storage sheds, locomotives, signals system, switches, and bridges. Under the constant specter of being caught by the Gestapo, Beiler travelled around the region handing out cans filled with a secret substance to railroad men whom he knew were loyal to the cause of ridding France of the Nazi yoke. The concoction in the cans had been created at a secret laboratory in London. If a railway man were halted by German sentries or Gestapo agents, the mixture appeared to be ordinary lubricating grease, a product the worker could be expected to carry. Actually, the substance was a highly abrasive compound that quickly wore out parts to which it was applied. Through use of the diabolical goo, Beiler’s clandestine group put ten locomotives out of action for long periods of time. Moreover, track workers were shown how to jam turntables with a single steel bolt, how to jam the gates at road crossings, and how to keep signals arms at “halt” when they should be at “proceed,” thereby stalling trains that were able to make short runs. Switchboard operators were taught how to immobilize a teleprinter circuit solely with a single feather in an armature. Along with air bombings, the undercover agents in northern France had largely immobilized the rail network and much of its rolling stock by the time the Allies were ready to invade on June 6.