PRR S1

Pennsylvania Railroad S1

Industrial designer Raymond Loewy stands on the front of the S1

Type and origin Power type Steam Builder PRR Altoona Works Serial number Altoona 4341 Build date 1939 Total produced 1

Specifications Configuration 6-4-4-6 UIC class 3′BB3′ Gauge 4 ft 8 1⁄2 in (1,435 mm) Leading dia. 36 in (914 mm) Driver dia. 84 in (2,134 mm) Trailing dia. 42 in (1,067 mm) Wheelbase Coupled: 26 ft 6 in (8.08 m), Loco: 64 ft 4 in (19.61 m), Loco & tender: 123 ft 9 1⁄4 in (37.73 m) Length 140 ft 2 1⁄2 in (42.74 m) Width 10 ft 7 in (3.23 m) Height 16 ft 6 in (5.03 m) Loco weight 608,170 lb (275,861 kilograms; 276 tonnes) Tender type 16-wheel tender (two 4-axle trucks) Firebox:  • Firegrate area 132 sq ft (12.3 m2) Boiler pressure 300 lbf/in2 (2.07 MPa) Cylinders Four Cylinder size 22 in × 26 in (559 mm × 660 mm) Valve gear Walschaerts

Performance figures Tractive effort 71,900 lbf (319.83 kN)

Career Operators Pennsylvania Railroad Numbers 6100 Retired 1945 Scrapped 1949 Disposition New York World's Fair in New York, scrapped in 1949.

The PRR S1 class steam locomotive (nicknamed "The Big Engine") was a single experimental locomotive, the longest and heaviest rigid frame reciprocating steam locomotive ever built. The streamlined Art Deco styled shell of the locomotive was designed by Raymond Loewy.

The S1 was the only locomotive ever built with a 6-4-4-6 wheel arrangement. It was a duplex locomotive, meaning that it had two pairs of cylinders, each driving two pairs of driving wheels. Unlike similar-looking articulated locomotive designs, the driven wheelbase of the S1 was rigid. The S1 was completed January 31, 1939 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 was too big for many PRR curves. Along with wheel slippage, this limited the S1's usefulness. No further S1 models were built as focus shifted to the T1 class.

In 1937 Pennsylvania Railroad officials decided to build a new passenger locomotive to replace its aging K4s locomotive. The PRR officials also hoped that the new S1 steam locomotive would have performance equal to their GG1 electric locomotive.

In a collaborative effort, the Pennsylvania Railroad, Baldwin Locomotive Works, the Lima Locomotive Works and the American Locomotive Company contributed to the experimental S1 design.

The S1 was the largest passenger locomotive ever constructed, with an overall length of 140 feet 2 ¹⁄₂ inches (42.74 m). At 77 feet (23.47 m) long and a weight of 97,600 pounds (44,300 kg; 44.3 t), the cast steel locomotive bed plate made by General Steel Castings was the largest single-piece casting ever made for a locomotive.