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.[1] 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) over engine and tender the
S1 could not negotiate curves on much of the PRR system.
This problem, along with wheel slippage, limited the S1's
usefulness. No further S1 models were built as focus shifted
to the T1 class. The last run for the S1 was in December
1945 and the engine was scrapped in 1949.
Courtesie Wikipedia