Western Maryland 2-6-6-2 "Mallet Mogul" Locomotives in the USA

Class M-1 (Locobase 8321)

Data from WM MISC steam locomotive diagram book supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. See also DeGolyer, Volume 41, pp. 328+. (Thanks to Chris Hohl for his 8 August 2016 email noting the original tender water capacity, incorrect building year and an apparent discrepancy between Baldwin and WM figures.) Works numbers were 33513-33514 in June 1909.

Comparisons with other 2-6-6-2s reveals that this design was virtually identical to that of the Great Northern's second batch of L-1s (Locobase 819), but with larger HP cylinders. Tender capacity later increased to 9,500 US gallons (35,980 litres) with a resulting loaded weight of 166,200 lb (75,387 kg).

Chris Hohl noted that the Baldwin's specs were considerably higher than those shown in Locobase. The Baldwin numbers are characterized with more than usual circumspection as "approximate". Also unusual was the large overestimate in both adhesion (estimated at 323,000 lb/146,511 kg) and engine weights (363,000lb/164,654 kg). Given the relative lack of experience with building large articulateds, it's possible that Baldwin was leaving itself some leeway.

Like the later Ls, these articulateds were dedicated to pusher service, which explains the lack of a superheater upgrade and the retention of slide valves.

According to Drury (1993), the class was converted to super-switchers (0-6-6-0s) in 1927-1931 that operated until scrapped in June 1944.

Class M-1a (Locobase 13938)

Data from WM MISC steam locomotive diagram book supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange and Baldwin Locomotive Works Specification for Engines as digitized by the DeGolyer Library of Southern Methodist University, Volume 41, p. 331. (Thanks to Chris Hohl for his 31 December 2017 email noting the original tender water capacity and weight.) Works numbers were 35300-35301 in October, 37140-37141 in October 1911, 37209-37211 in November 1911.

These were the slight enlargements of the design used in the 1909 pair of articulateds shown in Locobase 8321. Like the earlier engines, they were intended to roll on 86 and 90 lb/yard (43 and 45 kg/metre). Other than the small increase in boiler size caused by the inclusion of 13 more tubes, the two classes were essentially identical. All four cylinders were supplied through balanced slide valves.

The specs include a proviso apparently meant to foreclose any underhanded substitution of inferior components: "Locos to be built in the best, most substantial and workmanlike manner according to the true intent and meaning of these specifications, which are intended to include everything requisite to the proper building of the engine, notwithstanding that everything required is not particularly mentioned in these specifications."

Later tenders were bigger and carried 9,500 US gallons (35,958 litres) of water and weighed 166,200 lb (75,387 kg).

According to Drury (1993), the class was converted to super-switchers (0-6-6-0s) in 1927-1931 that operated into the late 1940s.