Denver & Rio Grande Western 4-6-6-4 "Challenger" Locomotives in the USA

The Denver & Rio Grande Western Railroad bought ten 4-6-6-4s from the Baldwin Locomotive Works in 1937 to speed up its freight trains. These locomotives were designated Class L-105 and were given road numbers 3700 through 3709. They had four 23 x 32 cylinders, 70" drivers, a boiler pressure of 280 psi, a tractive effort of 105,000 lbs and weighed 641,000 pounds.

Five additional Class L-105 "Challengers" arrived from Baldwin in 1942. These were similar to the Class L-105s bought in 1938 and were assigned road numbers 3710 through 3714.

In need of more locomotives to handle war-time traffic, the D&RGW ordered six more "Challengers". The War Production Board allowed six ALCO-built 4-6-6-4s to be delivered in 1943. The D&RGW did not like them, and leased them instead of buying them. These locomotives were designated Class L-97 and had four 21 x 32 cylinders, 69" drivers, a boiler pressure of 280 psi, a tractive effort of 97,350 lbs and weighed 627,000 pounds. In 1947, diesels were replacing many of the D&RGW's steam locomotives and the six Class L-97 "Challengers" were transferred to the Clinchfield Railroad.

There are no surviving D&RGW "Challengers".


ClassQty.Road NumberYear Built Builder Notes
L-105103700-37091938BaldwinNumbers 3700-3709 scrapped between 1951 and 1956
L-105 53710-37141942BaldwinNumbers 3710-3714 scrapped between 1951 and 1956
L-97 63800-38051943ALCONumbers 3800-3805 sold to the Clinchfield in 1947. Became Clinchfield Class E-1 and assigned road numbers 670-675. Clinchfield numbers 670-675 scrapped in 1953.

Class Details by Steve Llanso of Sweat House Media

Class L-105 (Locobase 339)

Data from D&GRW 1 - 1952 Locomotive Diagram supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. See also "New Motive Power for the Denver and Rio Grande Western Railroad," Baldwin Locomotives, Volume 16, No 4 (April 1938), pp. 3-9. Works numbers ran 62139-62148 in 1938.

Firebox had 200 sq ft (18.58 sq m) of heating surface in three thermic syphons and arch tubes. These were built for dual-service operation over the Continental Divide. The BL article said that the L-105 would confront grades of up to 3%, curves as tight as 16 deg (although the design could handle 22 degrees). A very detailed account of the components and materials can only be sampled. Metallurgical research resulted in a silicon manganese steel boiler. The 15-ft (4.57 m) long grate ended at a firebrick wall behind which was a cinder hopper, which, Locobase guesses, provided an alternative landing point for cinders that might otherwise clog the tubes or flues. Nine of the ten engines used Elesco feed water heaters; the tenth settled for the Worthington SA. 14" (356 mm) piston valves supplied each of the cylinders.

Of course, the bed was case as a single piece. A General Steel Castings front truck's wheels turned in roller bearings and enjoyed a swing of 6" (152 mm) to either side. Under the firebox, a Delta-type truck with 8" (203 mm) swing also used roller bearings.

An eastbound L-105 running the 64 miles (103 kph) from Salt Lake City to Thistle hauled 2,750 tons at 38 mph (61 kph), then over the Solider Summit on a consistent 2% adverse grade and using a helper at 18 mph (29 kph), then back up to 37.5 mph (60 kph) from Helper to Grand Junction.

Five more were supplied in 1942 with different tube and flue counts; see Locobase 1345.

Class L-105 (Locobase 1345)

Data from D&RGW 1 - 1952 Locomotive Diagram supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. Works numbers were 64178-64182 in November 1941.

This second group of five engines from Eddystone had smaller heating surfaces and consequently different ratios from the ten shown in Locobase 339. The engines were not exactly starved for quality heat, however, the firebox had 200 sq ft (18.58 sq m) of heating surface in three thermic syphons and arch tubes as well as 206 sq ft (19.14 sq m) in the combustion chamber. 3713's boiler sacrificed the syphons to accommodate Security circulators that contributed 138 sq ft (12.82 sq m) to a total direct heating surface area of 538 sq ft (49.98 sq m).

Elesco's Type T-501 exhaust steam injector preheated the boiler water, a Standard Type B automatic stoker delivered coal to the Hulson grate, and an American Throttle Company multiple throttle smoothed steam supply

A third group of six (3800-3805) L-97s were leased from the UP during World War II; see Locobase 16358.

Class L-97 (Locobase 16358)

Data from D&RGW 1 - 1954 Locomotive Diagram book supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. Works numbers were 70163-70168 in 1943.

In the midst of a large Union Pacific order for high-end Challengers (Locobase 341), the Rio Grande (or possibly the War Production Board) persuaded the UP to lease six of its order to the Colorado railroad. Other than a few tweaks to the heating surface areas, the design duplicated the UP engines.

After World War Two ended, the D&RGW returned the sextet to the UP. A year later in July 1947, the UP (or, technically, the Defense Plant Corporation) sold the set to the Clinchfield, which redesignated them as E-3s and renumbered them 670-675.

All were retired in August 1953 as part of an overall dieselization.

Principal Dimensions by Steve Llanso of Sweat House Media
Locobase ID339 1345 16,358
RailroadDenver & Rio Grande Western (D&RGW)Denver & Rio Grande Western (D&RGW)Denver & Rio Grande Western (D&RGW)
Number in Class1056
Road Numbers3700-37093710-37143800-3805
Number Built1056
Valve GearWalschaertWalschaertWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)12.17 / 3.7112.17 / 3.7112.17 / 3.71
Engine Wheelbase (ft / m)61.50 / 18.7561.50 / 18.7560.34 / 18.39
Ratio of driving wheelbase to overall engine wheebase 0.20 0.20 0.20
Overall Wheelbase (engine & tender) (ft / m)108 / 32.92106.67 / 32.51
Axle Loading (Maximum Weight per Axle) (lbs / kg)73,66974,721 / 33,893
Weight on Drivers (lbs / kg)437,939 / 198,674435,472 / 197,527404,200 / 183,342
Engine Weight (lbs / kg)641,900 / 301,639641,700 / 291,071627,000 / 284,403
Tender Loaded Weight (lbs / kg)394,000393,630 / 178,548437,000 / 198,220
Total Engine and Tender Weight (lbs / kg)1,035,9001,035,330 / 469,6191,064,000 / 482,623
Tender Water Capacity (gals / ML)20,000 / 75.7620,000 / 75.7625,000 / 94.70
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)26 / 23.6026 / 23.6028 / 25.50
Minimum weight of rail (calculated) (lb/yd / kg/m)122 / 61121 / 60.50112 / 56
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)70 / 177870 / 177869 / 1753
Boiler Pressure (psi / kPa)255 / 17.60255 / 17.60280 / 19.30
High Pressure Cylinders (dia x stroke) (in / mm)23" x 32" / 584x813 (4)23" x 32" / 584x813 (4)21" x 32" / 533x813 (4)
Tractive Effort (lbs / kg)104,833 / 47551.51104,833 / 47551.5197,352 / 44158.18
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.18 4.15 4.15
Heating Ability
Firebox Area (sq ft / m2)806 / 74.91806 / 74.88581 / 53.98
Grate Area (sq ft / m2)136.50 / 12.69136.50 / 12.68132.20 / 12.28
Evaporative Heating Surface (sq ft / m2)6341 / 589.315730 / 532.334795 / 445.47
Superheating Surface (sq ft / m2)2628 / 244.242525 / 234.582162 / 200.85
Combined Heating Surface (sq ft / m2)8969 / 833.558255 / 766.916957 / 646.32
Evaporative Heating Surface/Cylinder Volume206.04186.18186.89
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation34,80834,80837,016
Same as above plus superheater percentage44,90245,59848,491
Same as above but substitute firebox area for grate area265,134269,244213,111
Power L132,88931,40234,085
Power MT993.40953.851115.45

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Wes Barris