Western Pacific 4-6-6-4 "Challenger" Locomotives in the USA

Class M-100 (Locobase 343)

Data from WP-2 Locomotive Diagrams and WP All-Time Steam Locomotive Diagrams supplied in May 2005 and August 2013, respectively, by Allen Stanley from his extensive Rail Data Exchange collection. See also the 1947 Locomotive Cyclopedia and S Kip Farrington, Jr, Railroading Coast to Coast (New York: Bonanza Books, 1976), p. 123. Roster information from Frank Brehm's compilation hosted at [] (accessed 3 July 2006). Works numbers were 68902-68908 in January 1938.

Little-remarked group of Challengers for the WP that ran across the desert from Elko, Nevada to Salt Lake City, Utah. The data convey in many ways just how big a Challenger the 401 truly was.

The Western Pacific's diagram book contains a few more: boiler water capacity with one gauge of water was 7,750 US gallons (29,334 litres). 2 gauges full equated to 8,310 gallons (31,453 litres), and 3 gauges meant 8,840 US gallons (33,459 litres). Locobase can't resist comparing those oceans of water to a swimming pool and calculates that a 3-gauge boiler would fill a oval pool 40 feet long, 8 feet wide, and 9 feet deep (12.2 x 2.44 x 2.74 m).

Four thermic syphons contributed 151 sq ft (14.03 sq m) to the direct heating surface. Each cylinder was fed by its own 12" (305 mm) piston valve. The four wheels of the leading truck turned ASF roller bearings, while the six-wheel trailing truck used SKF rollers. The WP installed thermic syphons in the combustion chamber in at least 401, 403-404.

Very similar to the Clinchfield and D&H locomotives running on this wheel arrangement. See Locobase 338 for a description of the revised bearing design that permitted smooth riding at much higher speeds than usually reached by articulated locomotives. Even before that update, S Kip Farrington, Jr's note in a 29 May 1940 engine log said the 402 hauled 57 cars aggregating 2,780 tons (2,527 tonnes) "extremely well taking the Wendover hill, 68 miles (109 km) of 1%, with ease."

Each of these engines cost $181,762 on delivery in 1938. Fourteen years later, supplanted by diesels, their scrap value amounted to $13,762 apiece in May and June 1952.