From TrainSpottingWorld, for Rail fans everywhere
Profile view of the S1
Power type Steam
BuilderPennsylvania Railroad
Build date1939
Total production1
Gaugeft 8½ in (1435 mm)
Driver size84 in (2.13 m) diameter
Total weight608,170 lb.
Boiler pressure300 lbf/in² (2.07 MPa)
Fire grate area132 ft² (12.3 m²)
Cylinder size22×26 in (559×660 mm)
Valve gearWalschaert
Tractive effort71,900 lb.
CareerPennsylvania Railroad
Number in class1

The Pennsylvania Railroad's class S1 comprised a single steam locomotive of 6-4-4-6 wheel arrangement in the Whyte notation, the only locomotive of such arrangement ever constructed. The S1 was a duplex locomotive: it had two pairs of cylinders, each driving two pairs of driving wheels, but its driven wheelbase was rigid, unlike similar-looking articulated locomotive designs. The locomotive was displayed at the New York World's Fair of 1939, lettered American Railroads rather than Pennsylvania Railroad. The streamlined shell was designed by Raymond Loewy.

The S1 was the largest express passenger locomotive ever constructed, and its cast steel locomotive bed by General Steel Castings was the largest ever made. The six-wheel leading and trailing trucks were added as the locomotive's design became too heavy for four-wheel units, but the locomotive was still overweight by a significant margin. The vast boiler was the largest the PRR ever built. The locomotive was so large, in fact, that it could not fit on most of the PRR system. In its brief service life it was restricted to the main line between Chicago, Illinois and Crestline, Ohio; it was based at the Crestline enginehouse. For display at the New York World's Fair, it took a circuitous route over the Long Island Rail Road; many obstacles had to be temporarily removed, and others passed at a slow crawl.

Crews liked the S1, partly because of its very smooth ride. The great mass and inertia of the locomotive soaked up the bumps and the surging often experienced with duplex locomotives.

It was hoped that the locomotive could haul 1,000 tons at 100 miles per hour, but this goal was not reached. Furthermore, the locomotive's extreme length limited its usefulness as it was incapable of negotiating curves on most lines of PRR track. No further S1s were built. PRR instead turned its attention to the T1 class of 4-4-4-4 duplex locomotives, but they also met with limited success.

Its high speed capability was such that some have claimed the S1 may have even exceeded the 126 mph record steam locomotive speed set in 1938 by the LNER locomotive Mallard.[1] However, it appears that no verifiable records are available to authenticate the claim.

The S1 appears in the Sandman comic series, book IX.

A locomotive resembling the PRR S1 pulls the train in the "Billion Dollar Limited" episode of the 1940s "Superman" cartoon series.

See also