2-8-8-8-4

Under the Whyte notation for the classification of steam locomotives, a 2-8-8-8-4 has two leading wheels, three sets of eight driving wheels, and four trailing wheels.

Other equivalent classifications are: :UIC classification: (1′D)D(D2′) : French classification: 140+040+042 : Turkish classification: 45+44+46 : Swiss classification: 4/5+4/4+4/6

Only one 2-8-8-8-4 was ever built, a Mallet-type for the Virginian Railway in 1916.{{cite web|last1=Self|first1=Douglas|title=Triplex Locomotive |author-link=Douglas Self |access-date=8 May 2016}} Built by Baldwin Locomotive Works, it became the only example of their class XA, so named due to the experimental nature of the locomotive. Like the same railroad's large articulated electrics and the Erie Railroad 2-8-8-8-2s, it was nicknamed "Triplex".

The XA was unable to sustain a speed greater than five miles an hour, since the six cylinders could easily consume more steam than the boiler could produce. When operating in compound the high pressure steam was divided between the cylinders of the center engine. The exhaust from one cylinder was piped to the front articulated engine. The exhaust from the other center engine cylinder was piped to the tender engine.

The exhaust from the front engine was piped to the exhaust nozzle inside the firebox to generate draft through the firebox, through the fire tubes and out the exhaust stack. The exhaust from the tender engine went out of a stack at the rear of the tender water tank. Unfortunately it did not contribute to draft, being wasted. The tender had a four-wheel truck at the rear to help guide the locomotive into curves when drifting back downhill after pushing a train over the hill.

The XA was sent back to Baldwin in 1920 after World War 1 and was rebuilt as two locomotives, a Class AF number 610 and a Class MD number 410 . Unlike their predecessor which lasted only a few years in service from 1916-1920/1921, these two separate locomotives remained in service pulling freight trains until 1953. However, neither of the two locomotives were preserved they were scrapped after Diesel Locomotives were brought by the Virginian Railroad from EMD,GE and AlCo after World War 2 .

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