Norfolk and Western 2156

Norfolk & Western 2156 is the sole survivor of the railroad's Y5, Y6, Y6a and Y6b classes (in final form referred to as the "Improved Y5/Y6 class"). These locomotives developed 152,206 pounds of tractive effort when built, with later modifications bringing them closer to 170,000 pounds. By comparison, the Union Pacific Big Boy locomotives developed 135,375 pounds-force (602.2 kN) of tractive effort. The only successful steam locomotives that developed somewhat more tractive effort, the Virginian AE class 2-10-10-2s, pulled trains at about 8 mph (13 km/h), while the N&W Y6's regularly pulled trains 50 mph (80 km/h), and some anecdotal evidence exists that they pulled trains up to 63 mph (101 km/h).

N&W 2156 is also one of the Y6a's that received a new firebox with an extended combustion chamber of the type used on the Y6b class, which increased drawbar horsepower from 4,400 hp (3.3 MW) at 20 mph (32 km/h) to 5,600 hp (4.2 MW) at 25 mph (40 km/h).

Coal traffic was N&W's largest source of revenue, and it had arguably the most modern and efficient steam locomotives of any major U.S. railroad. Accordingly, N&W resisted conversion from coal-burning steam locomotives to oil-burning diesels longer than most. In 1952, N&W tested its A-class and Y6b-class locomotives against a four-unit Electro-Motive Division F7 diesel set. The tests indicated that fuel costs and similar items were roughly the same, and the test was considered a tie. However, diesels eventually won out for lower maintenance and other operational costs.

Retrospective analyses of these tests have led to suggestions that diesel locomotive builder EMD and N&W cheated in the competition by using locomotives with secret modifications unsuited for daily work.[1][2] However, the greater weight of evidence and analysis indicates that N&W did not cheat on these tests, and that the only improvements were the ones N&W publicized and later incorporated into many locomotives.[3][4] Also, the major participants in this debate all appear to agree that N&W did ultimately modify most of its Y5, Y6, Y6a, and Y6b locomotives (including N&W 2156) with a new "intercepting/reducing valve" and ballast on the front engine, which increased their tractive effort.[5]

Norfolk & Western used 2156 and the other Y6-class locomotives primarily for slower, heavy freight trains in the more mountainous districts in the Pocahontas, Radford and Shenandoah Divisions. They mostly hauled manifest freight and coal trains.[6]

When diesel locomotives took over the mainline steam operations, the Y6-type locomotives spent their last two years mostly on mine and other coal-field runs.

In July 1959, N&W donated 2156 to the National Museum of Transportation.[6]

The museum cosmetically restored the locomotive in 1985.[6]

In 2014, the museum agreed to lease the locomotive to Norfolk Southern and the Virginia Museum of Transportation in Roanoke, Virginia, in return for an EMD FT B unit.[7] On May 9–12, 2015, the locomotive was towed to its temporary home.

On May 31, 2015, 2156 was reunited with N&W Class A No. 1218 and the recently restored Class J No. 611 as N&W's "The Big Three".[8][9]

On June 10, 2020, 2156 left the Virginia Museum of Transportation in Roanoke, VA to go back to the St. Louis Museum of Transportation.[10] It arrived back at the St. Louis Museum of Transportation on June 15, 2020. The locomotive remains on static display in St. Louis as of 2023.