Curiously, of all the lines which may been interested in the 2-6-6-4 it was a southern system which purchased the wheel arrangement next. A year after the P&WV acquired its first example the Seaboard Air Line went to Baldwin and ordered a small roster of five in 1935. Numbered 2500-2504 and listed as Class R-1 the locomotives were simple expansion designs featuring Baker valve gear, tractive efforts above 82,000 pounds, and rated at 2,700 tons. Two years later Seaboard went back to Baldwin for a secondary order, Class R-2 #2505-2509 that utilized Walschaert valve gear but for the most part were very similar to the R-1s. According to the article, "Twin Stacks, 'Ready Boys? I'm Going To Wind Her Up'" from the August 1979 issue of Trains the 2-6-6-4s were the largest steamers ever used by the Seaboard, whose earlier 2-8-8-2s were not very well liked and sold to the Baltimore & Ohio.
Along with the Clinchfield the Seaboard was the only southern road to use articulated steam in the Deep South. While the SAL's R-1s and R-2s might be considered less powerful than other versions of the design (such as the P&WV's or N&W's) they are often regarded as the first articulateds built for high-speed operation sporting 69-inch drivers. Overall, the locomotives were said to be well-liked by SAL crews who were somewhat disappointed in having to operate the big steamers at slower speeds than they were capable of running. After just a decade of service the Seaboard sold their fleet to the B&O, which reclassified them as KB-1/a and used them in fast-freight service along the eastern end of the Cumberland Division between Cumberland and Brunswick, Maryland where grades were relatively flat in the Potomac Valley.
The Norfolk & Western, of course, made the 2-6-6-4s famous when it
began outshopping its Class As in 1936 built in Roanoke, Virginia. In
all the N&W would roster forty-three examples, numbered 1200-1242,
that were clearly the finest ever built. Normally, the railroad used
them along its Pocahontas Division in West Virginia as well as running
through Portsmouth, Ohio and Columbus. According to SteamLocomotive.com
the Class As were rated at 13,000 tons in slow drag service (with a
tractive effort surpassing 125,000 pounds) but could also pull a
passenger consist at an incredible 70 mph! The locomotives remained in
service until steam finally ended on the N&W in 1959. Finally, of
note was the 2-6-6-4 designed by Baldwin but never built for the Erie.
Had it taken place, the railroad would have been operating the big
Mallet five years prior to anyone else.
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