Pennsylvania Railroad class S1

Common card · No. 245327

The PRR S1 class steam locomotive (nicknamed "The Big Engine") was a single experimental duplex locomotive of the Pennsylvania Railroad. It was designed to demonstrate the advantages of duplex drives espoused by Baldwin Chief Engineer Ralph P. Johnson. The streamlined Art Deco styled shell of the locomotive was designed by Raymond Loewy. The S1 had a unique 6-4-4-6 wheel arrangement, meaning that it had two pairs of cylinders, each driving two pairs of driving wheels. To achieve stability at fast passenger train speeds (above 100 mph), articulation was not used. The S1 was completed on January 31, 1939, at Altoona shop, and was numbered 6100. At 140 ft 2+1⁄2 in (42.74 m) overall, engine and tender, the S1 was the longest reciprocating steam locomotive ever; it also had the heaviest tender (451,840 lb (204.95 t)), highest tractive effort (76,403 lbf (339.86 kN)) of a passenger steam engine when built and the largest driving wheels (7 feet in diameter) ever used on a locomotive with more...

Read on Wikipedia · Image University of Southern California Library/California Historical Society, CC BY 3.0