The S-2 Steam Turbine Type 6-8-6 Locomotive No. 2020 was based on a prototype built by the Pennsylvania Railroad. This engine was deemed inefficient by this railroad and they only made one of them. However, in the "euphoria" of post-war toy train production, Lionel made thousands of them!

Produced from 1946 until 1949, this locomotive did not have magnetraction and it usually came with either No. 2020W or 2466WX tenders that had a whistle and came with staple-end trucks with one electronic coupler.

This locomotive came with a smoke unit, headlight, and was controlled by a three position directional unit whose control lever is adjustable from just in front of the cab. There is a Keystone decal on the front that is numbered "6200". This locomotive is equivalent to the 0 Gauge No. 671 and this, and other versions of locomotive that were produced by Lionel for O and O27 Gauge sets run best on the larger diameter O Gauge track.

There are six variations:

Variation A: Directional Unit and whistle in tender are connected by jacks to the motor that was labeled "ATOMIC MOTOR" in the locomotive. A double worm drive provides the power to the drive axles. In the front of the locomotive is a RED Keystone that has GOLD lettering, and is rubber-stamped "6200". This number is often found missing due wear and handling. On the sides, this version is equipped with shinny nickel rims on the drive wheels. Came with a No. 2020W tender that has WHITE rubber-stamped "LIONEL LINES" lettering on the sides and has grab railings on the sides and the deck. 1946 production. Some tenders are found with the rubber-stamped number on the bottom and these were probably produced in 1947 or 1948.

Variation B: Identical to Variation A, but came with No. 2466WX tender, and it has a BLACK Keystone on the front with WHITE number "6200" heat-stamped. (1946)

Variation C: Has an on-board directional unit whose lever protrudes though the top of the boiler and a single worm drive motor that is labeled "LIONEL PRECISION MOTOR" that no longer has the jacks. The Keystone is a RED numbered "6200" decal on the front of the locomotive, and the No. 2020W tender has a whistle that has a plastic housing, and came with all of the railings that were on the previous issues. (1947)

Variation D: Similar to Variation C, but with blackened steel rims on the drive wheels and came No. 2020W or No. 6466WX tender. (1948)

Variation E: Similar to Variation D, but without steel rims on the drivers. (1948)

Variation F: Identical to Variation A, except the motor brush plate is made out of Bakelite and is RED in color. Manufactured in late 1946 and early 1947, these brush plates are also found on the No. 726 Berkshire’s and No. 2332 GG-1’s.