Lionel, American Flyer and Marx were just emerging from their wartime hiatus. All three were entusiastic to resume toy production. They also wanted to have the kind of new models that would dazzle potential customers. Lionel seized on the S2 turbine and had one ready to sell by 1946. That was the first of the #671 types. During the 1950s, Lionel produced other versions of its 671, along with the O27 model 2020 and followed by 681 and 682. Obviously, the S2 turbine was a big seller for Lionel. It was reissued again years later, as were versions by Williams and MTH.
You might bet the impression that the S2 turbine was a great success. As far as Lionel was concerned, it was. Things were not so rosy for the Pennsylvania Railroad. At high speed, the steam turbine was wonderful. The problem was at low speed and idling. The S2 gluttonously consumed coal. Since trains spend a lot of time at low speed and stopped in yards and stations, the S2 was just too expensive to justify its advantages. The turbine-powered locomotive was a flop. A dud. A clunker. It was eventually scrapped. And though the Pennsy used steam well into the 1950s, diesel had the upper hand.
Most folks who run classic O gauge have an S2 or two lurking around the train room. I have two: a 671 and a 2020. Despite its O27 designation, by the way, the 2020 is the same size and pretty much the same everything else as the 671. For O gaugers, the S2 is one of the iconic pieces that define the hobby.
From 2001 to 2011, I participated in a train display at Ocean Grove, NJ, during their Victorian Holiday festival in the middle of December. Several locomotives were popular with the visitors. The little bright blue plastic Jersey Central steamers from the early MPC era were a hit, as this is central NJ. The folks also liked the Railking Chessie F3 and the Marx M10000 (cherry red with only two units, no less) and tinplate Marx steamer with its consist of tin NYC passenger cars. The one locomotive which awed them was the S2. Its size and heft and the "clank-clank" of its drive bar enthused young and old alike. Though it flubbed for the Pennsy, the S2 was still an O gauge winner after all these years.
Here is a book touting Pennsylvania Railroad motive power:
(671, 681, 682 and 2020 are Lionel model numbers, usually printed on the cab beneath the engineer’s window. The Pennsy designation of the locomotive was S2 and gave it the road number 6200)