The Great Northern Railway 1908 "B" Class 4–8–2 Mountain type steam locomotives were workhorses of the Great Northern Railway. These engines had the heaviest main frames ever made in the US, weighed 305 tons fully laden, and were outfitted with 25x30 cylinders, 73-inch drivers, and a 285 p.s.i. boiler pressure. Each had a total tractive effort of 61,584 pounds and could haul 2,618 tons of freight at a maximum speed of 40 mph. The engines could also pull up to 16 passenger cars at up to 65 mph. Originally designated Class J, their designation was eventually changed to Class B.
The design of William Kratville and George Estby, the first of the 1908 "B" class engines was delivered from the Baldwin Locomotive Works on March 17, 1908, and the last of the thirty engines was delivered the following December. All of the engines served the Great Northern Railway until being retired in the 1952-1959 time frame.