French National Railways No. 232.U1

Shortly before the outbreak of war in 1939, the Northern Region of the French National Railways (S.N.C.F.) placed in service seven 4-6-4 express locomotives designed by Monsieur de Caso and designated Classes ' R ' and ' S.' The eighth engine was to have been a Lungstrom turbine, but due to the war this was never carried out and the locomotive entered service after the war as a modified Class ' S ' 4-cylinder compound numbered 232.U1.

Ul may be regarded as the last word in French steam locomotive design, and probably the most advanced steam engine in the world. Basically it is a de Glehn compound with the difference that the high-pressure cylinders are between the frames; for ease of maintenance the Dabeg poppet valves of the other 4-cylinder compounds were omitted and Walschaerts valve gear, with a conjugated drive to the inside cylinders, was employed.

Also, unlike most compound engines in France, the respective cut-offs were not independently variable; they remained at a fixed ratio. However, through a system of servomotors and air-operated regulators, the locomotive started as a 4-cylinder simple and automatically changeg over to compound working as speed was gained.

Other refinements included a Standard 3-jet stoker, feed water heater, roller bearings on all axles, brakes on bogie and trailing wheels, and self-adjusting axleboxes; the latter, combined with equalized springing, assured magnificently smooth riding.

232.Ul spent her entire life based at La Chapelle depot in Paris, working high-speed expresses north to Aulnoye and Lille; after these services were taken over by electric traction, Ul was scheduled for museum preservation.