A visit to the Norfolk & Western in the early 1950s was like a scene from Jurassic Park: prehistoric beasts romping in their natural mountain habitat. At a time when other roads were letting their remaining steam engines rot away and giving them minimal service in dirty, dingy, soon-to-close facilities, the N&W was still running a first-class steam operation and even building new power. With its main line through some of the nation's richest coalfields, it was still betting on the future of steam; as late as 1955, the N&W didn't roster a single diesel. The majority of traffic was handled by what N&W fans call the "holy trinity of steam": the streamlined Class J Northern; the articulated greyhound Class A; and the massive Y6b 2-8-8-2, "the workhorse of the N&W."

Built in the N&W's own Roanoke shops from 1948-52, the Y6b was the final evolution of the USRA Heavy Mallet, designed at the N&W's request in 1918. Unlike most modern articulated locomotives, which were "simple expansion" engines that used high-pressure boiler steam in all four cylinders, the Y6b followed Anatole Mallet's original idea. Like all true Mallets, the Y6b was a compound articulated that used steam twice: first in the smaller, high-pressure cylinders of its rear engine, and then again in the larger, low-pressure cylinders of its front engine before exhausting up the stack.

"Long after everybody else gave up the Mallet as an impossibly slow beast of burden," wrote Trains magazine editor David P. Morgan, "N&W kept tinkering with the design it had once loaned to other roads in the guise of the USRA compound 2-8-8-2 until it had that ideal mountain engine, the Y6. (And if anybody ever manages to locate the figures to compare N&W's compounds with anybody else's simple articulateds in mountain service, I'd lay my money on using steam twice.)" As Morgan noted, the Y6b was "one of those unique compounds that can be worked simple (high-pressure steam to all four cylinders) up to 10 mph [to start a heavy train], and thereafter still get a shot of 300-pound boiler steam for the fat low-pressure cylinders up front if the going get rough." He called it "the piece de resistance of any Norfolk & Western roundhouse, a loud-mouthed, squat-drivered monster that weighs 495 tons, requires a 115-foot turntable, and can hit 50 mph." Like the Swiss Crocodile shown elsewhere in this catalog, the Y6b was a mountain goat bred for heavy loads, steep grades, and winding curves.

For 2010, the Y6b returns to the RailKing Imperial line, equipped with twin motors and speed control to match the prototype's pulling power at any speed. Imperial features that set this model apart include legible builders plates, tender truck safety chains, crew figures, cab interior light, painted backhead gauges, and a real coal load in the tender.