The engines and tanks required for some scenes made so much noise that "action" and "cut" were signaled by codes on the engines' whistles.
The filmmakers hired a train to carry their equipment from one location to another, and this is the train we see as the art train in the film.
The primary steam locomotives in the film are Class 230Bs, #739 (leads the military train Paris to Vaires), 517 (art train until Rive-Reine crash), 855 (rear engine in Rive-Reine crash), and 711 (art train post-crash). These engines were built from 1901 to 1912, and were nearing the end of their long service life in 1964.
The sequence in which Burt Lancaster evades an air attack on his locomotive by driving at full speed into a tunnel was based on an attack on the Great Western Railway during the war. A passenger train was pursued by a German fighter along the main line into Wales. Reaching speeds estimated at 90 mph (well above the wartime restrictions in place) the train successfully escaped into the tunnel under the River Severn in Gloucestershire and stopped beneath the river until the engineer judged that the danger had passed. The train was struck several times during the chase but there were no serious injuries.