Burt Lancaster performed all his own stunts in this movie. Albert Rémy also got into the act by performing the stunt of uncoupling the engine from the paintings train on a real moving train.
Burt Lancaster took a day off during shooting to play golf when the production was about half completed. On the golf course, he stepped in a hole and re-aggravated an old knee injury. In order to incorporate the real injury into the film, John Frankenheimer had Lancaster's character shot in the leg, thus enabling him to limp through the rest of the shooting.
In reality, the museum's paintings were indeed loaded into a train for shipment to Germany, but fortunately the elaborate deception seen in the movie was not really required. The train was merely routed onto a ring railway and circled around and around Paris until the Allies arrived.
The engine that crashes into a derailed engine was moving at nearly sixty miles per hour. The crash was staged in the town of Acquigny, with extensive safety precautions and special insurance. Only one take was possible, and seven cameras were used.
The budget doubled under John Frankenheimer, due to an emphasis on action and the filming of train wrecks, eventually reaching $6.7 million. United Artists felt compelled to step in and assert its completion rights, demanding that principal photography be finished in seven weeks.