The Duluth, Missabe & Iron Range Yellowstones were built in two classes by the Baldwin Locomotive Works in Philadelphia, PA: eight M3 class in 1941 (#220-227) and ten M4 class in 1943 (#228-237).
This type of locomotive took its name from the "Yellowstone Route", the name of the Northern Pacific line, the railroad which ordered the first
2-8-8-4s from Alco in 1928. No NP Yellowstones have survived, but there are three DM&IR Yellowstones left in the US. As well as M3 #225 on this page, you can see M3 #227 on the Lake Superior Railroad Museum page and M4 #229 on the Two Harbors, Depot Museum page.
#225 is on display just off US Highway 2 in Proctor, MN. I have visited several times and the photos on this page are from various dates.
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With the approach of WWII, the DM&IR faced some challenging freight requirements. Iron and steel would be crucial to the war effort and the railroad would need locomotives capable of hauling long (115 car plus) trains of 8,750 tons or more on 0.62% grades without stalling.
The Western Pacific's oil-burning M-137 class
2-8-8-2, also built by Baldwin, formed the basis for DM&IR's M3 design, but a slightly larger coal burning firebox and an all-weather enclosed cab necessitated a longer frame with a four wheel trailing truck.
Timken roller bearings were fitted to all driver axles and ASF roller bearings to all truck axles,
and these were the only Yellowstones to be
mated to rigid frame 4 + 10 truck "centipede" tenders like those used on the Union Pacific's
Big Boys. The tender weighs 438,000 lbs light
with a capacity of 25,000 gallons of water and 26 tons of coal.
The first eight M3s cost $246,570 each. All the DM&IR Yellowstones were fitted with Baker
valve gear, the only application to the Yellowstone type.
The overall locomotive wheelbase is 113' 6",
engine wheelbase 67' 2" and each driver
wheelbase 17' 3". The drivers are 63" and the cylinders 26" x 32".
With a 125 sq ft grate and 750 sq ft firebox, the total heating surface of 9,552 sq ft included 194 sq ft in three thermic syphons, 177 sq ft in the combustion chamber, 32 sq ft of arch tubes and 2,770 sq ft superheating provided by a Type E superheater with two hundred and forty-five 21' long 3¾" flues. Operating at a boiler pressure of 240 psi, it delivered 140,093 lbs tractive effort.
Ore trains ran downhill from the Mesabi and Vermillion Ranges to docks in Duluth or Two Harbors, and these trips did not require much of the Yellowstones. It was returning empty ore cars from Duluth up the 2.2% grade to the yards in Proctor that used their full pulling power.
During its twenty-one years service, #225 hauled over 44,000,000 tons of iron ore, travelling a total of 694,360 miles. Before retiring in 1961, it also hauled a number of railfan excursions. The DM&IR donated #225 to the city of Proctor on 25th March 1963.
Prior to putting the new Yellowstones into service, the DM&IR invested heavily in capital improvements, including new engine houses and turntables to accommodate the 128' long locomotives, new tools and shop equipment and raising water standpipes to supply the 14' high tender manholes.
115 lb rail was installed on the southbound track to Two Harbors, MN, to take the 560,257 lb weight of the locomotive, and adjacent tracks were re-spaced on some curves to allow the required lateral clearance for the long boilers.
When built, the DM&IR Yellowstones sported dark green boiler and smokebox jackets. DMIR M3 #227 still has its jacketing, and you can see photos of it on the Lake Superior Railroad Museum page of this website.
In 1995, #225's original jacket and cladding were removed. This made it less susceptible to water penetration and deterioration in the damp lake-shore air. Note the Elesco Feedwater Heater in front of the smoke stack: M3s #220-#222 were fitted with Worthington feedwater heaters, #223-#227 with Elescos.
Although often referred to as Mallets, the DM&IR Yellowstones were not true Mallets. A Mallet
reuses steam from the first set of cylinders in larger, lower pressure cylinders, usually at the front of the locomotive. This process, called compound compression, was first applied commercially by the Swiss engineer Anatole Mallet (1837-1919) in 1876 to a series of small, 2 cylinder compound 0-4-2 tank locomotives for the Bayonne-Anglet-Biarritz Railway in France.
Mallet also introduced locomotive articulation, in which the rear engine is rigidly attached to the main body and boiler of the locomotive, while the front engine rides on a separate truck attached to the rigid rear frame by a pivot so that it can swing from side to side. Above, two photos of the pivot connection on #225.
Photos on the right: to make this work, the front end of the boiler rests on a sliding bearing on top of the swinging front truck. The bolster fitted beneath the front end of the boiler does not provide any support on the front engine frame for the boiler’s weight. As the locomotive takes curves, the bolster slides over the plate fixed to the front frame.
Above, exhaust from the front cylinders is piped to the smokebox via a rotating ball joint.
Articulateds were suited to narrow gauge railways, but were also useful where high tractive effort was needed, such as the DM&IR. After the 1920s, most four cylinder articulated locomotives were designed to supply steam directly to both sets of cylinders in a process called simple expansion, and many railroads also converted existing compounds to simple. As it uses simple expansion, #225 should really be referred to as an articulated locomotive rather than a Mallet.