|Norfolk & Western 2156|
|Builder||N&W's Roanoke Shops|
|Build date||March 19, 1942|
|UIC classification||(1′D)D1′ hv4|
|Gauge||4 ft 81⁄2 in (1,435 mm)|
|Leading wheel diameter||30 in (762 mm)|
|Driver diameter||58 in (1,473 mm) (as built 57 in (1,448 mm))|
|Trailing wheel diameter||30 in (762 mm)|
|Weight on drivers||548,500 lb (248.8 tonnes)|
|Locomotive weight||611,500 lb (277.4 tonnes)|
|Locomotive and tender combined weight||990,100 lb (449.1 tonnes) (as built 961,500 lb (436.1 tonnes))|
|Fuel capacity||60,000 lb (27.2 tonnes)|
|Water capacity||22,000 US gal (83,000 l; 18,000 imp gal)|
|Boiler pressure||300 psi (2.07 MPa)|
|Fire grate area||106.2 sq ft (9.87 m2)|
|Superheater area||1,478 sq ft (137.3 m2)|
|Cylinders||Four: two low-pressure (front), two high-pressure (rear)|
|25 in × 32 in (635 mm × 813 mm)|
|39 in × 32 in (991 mm × 813 mm)|
|Tractive effort||166,000 lbf (738.4 kN) (as built 152,206 lbf (677.0 kN))|
|Career||Norfolk & Western Railway|
|Number in class||2 of 16|
|Locale||United States, South and Midwest|
|Current owner||Museum of Transportation, St. Louis, Missouri|
Norfolk & Western 2156 is the strongest-pulling extant steam locomotive in the world, although it is not operational. It is a four-cylinder compound articulated (Mallet) locomotive with a 2-8-8-2 (Whyte notation) wheel arrangement. The Norfolk & Western Railway built it in 1942 at its Roanoke Shops in Roanoke, Virginia, and it was part of the Norfolk & Western's Y6a class. It was retired from regular rail service in July 1959, and today it is at the Museum of Transportation in St. Louis, Missouri, U.S.A.
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 were among the hardest-pulling steam locomotives ever built. They were originally rated for a tractive effort of 152,206 pounds-force (677.0 kN), and improvements in the 1950’s resulted in most of these locomotives (including N&W 2156) having their tractive effort increased to a measured 166,000 pounds-force (738.4 kN), which necessitated adding about 28,000 pounds (12.7 t) of lead to the front engine frame, to improve traction. (By comparison, the famous Union Pacific Big Boy locomotives developed 135,375 pounds-force (602.2 kN) of tractive effort.) This pulling power is all the more remarkable insofar as 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 successfully 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 4400 hp (3.3 MW) at 20 mph (32 km/h) to 5600 hp (4.2 MW) at 25 mph (40 km/h).
No discussion of N&W 2156 and its siblings would be complete without referring to their epic contest against new Diesel locomotives in 1952, and the related modifications to the locomotives, which have been a source of some debate among rail historians. N&W had coal traffic as arguably its most important 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 major railroads. In 1952 N&W tested its A-class and Y6b-class locomotives against a four-unit Electro-Motive Division (at that time, of General Motors) F7 Diesel set. The tests indicated that fuel costs and similar items were roughly the same, and the test was considered a tie. However, eventually Diesels won out for lower maintenance and other operational costs.
Retrospective analyses of these tests have caused a few, even in published articles by knowledgeable historians, to assert that Diesel-locomotive-builder EMD and/or N&W used secretly-modified locomotives for these tests. If N&W's modified Y6b locomotive number 2197, in addition to its publicized improvements, had received secret upgrades that would not be appropriate for daily-use locomotives, then the claims of substantially upgraded performance were something of a fraud. 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 significantly increased their tractive effort.
Norfolk & Western used 2156 and the other Y6-class locomotives primarily for slower, heavy freight trains in the more mountainous districts. Although they were used throughout the N&W, their primary work occurred on the Pocahontas, Radford, and Shenandoah Divisions. They mostly hauled manifest freight and coal trains.
When Diesel locomotives took over the main-line steam operations, the Y6-type locomotives spent their last two years mostly on mine and other coal-field runs. During this period, specifically in July 1959, N&W donated 2156 to the Museum of Transportation.
Today N&W 2156 is one of the attractions at the Museum of Transportation in St. Louis. She sits cosmetically restored, but she has not operated in several decades. Although there is some sentiment for restoring 2156 to operational condition, doing so would be a massive undertaking that, even if possible, would probably cost millions of dollars and take years to complete.