Norfolk and Western 2156

Norfolk and Western 2156 is a preserved Y6a class 2-8-8-2 compound Mallet steam locomotive. The Norfolk and Western Railway (N&W) built it in 1942 at its own Shops in Roanoke, Virginia as the second member of the N&W's Y6a class. No. 2156 and its class are considered to be the world's strongest-pulling extant steam locomotive to ever be built.

No. 2156 was retired from revenue service in July 1959, and it is now owned by the National Museum of Transportation in St. Louis, Missouri. In 2014, the museum leased it for five years to the Virginia Museum of Transportation in Roanoke. It was towed to Roanoke in May 2015, and then it was towed back to St. Louis in June 2020.

Historic significance
Norfolk and 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 135375 lbf 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, while the N&W Y6's regularly pulled trains 50 mph, and some anecdotal evidence exists that they pulled trains up to 63 mph.

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 4400 hp at 20 mph to 5600 hp at 25 mph.

Steam versus diesel tests, upgrades, and controversies
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. 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. 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.

Operational history
The N&W 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.

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.

Preservation years
In July 1959, N&W donated 2156 to the National Museum of Transportation (MoT), and the locomotive was put on static display at their property in St. Louis, Missouri. In 1985, No. 2156 received a cosmetic restoration performed by members and volunteers of the St. Louis Steam Train Association, with the intention of having the locomotive displayed at the St. Louis Union Station during the building's renovation ceremony. In August that same year, restoration work was completed, and No. 2156 was temporarily displayed at the station next to Union Pacific EMD E9 No. 951.

In 2014, the MoT agreed to lease No. 2156 to Norfolk Southern and the Virginia Museum of Transportation in Roanoke, Virginia, in return for an EMD FT B unit. 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". On June 10, 2020, 2156 left the Virginia Museum of Transportation in Roanoke, VA to go back to the St. Louis Museum of Transportation. 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.