Imperial Government Railways Articulated Locomotives in Japan


Class Details by Steve Llanso of Sweat House Media

Class 4600/9750 (Locobase 10974)

Data from [], and 1922 Locomotive Cyclopedia, p.1016. See also Akira Saito, "A Summary of Overview of Japan's Modern Steam Locomotives", based on his May 2000 Rail Magazine article and available on the web from 2004 at [] . Schenectady works numbers were 51946-51969 in 1912.

Alco's home plant in Schenectady, NY, turned out this batch of Mallets in 1912 as part of a big splurge on compound articulated locomotives that were hoped to "solve a big bottle neck at Hakone-pass, the most important trunk line." Alco had already supplied six 0-4-4-0 Mallets, a small design Saito dismisses as training vehicles.

He speculated that Yasujiro Shima, the JGR's well-known motive power exponent, wouldn't have accepted "imports that had not been technically evaluated" by JGR's locomotive engineers." But Shima was in Germany at the time and couldn't counter "aggressive" sales tactics on the part of three major locomotive builders--Baldwin, Henschel, and Alco. Indeed, "importation circumstances were really vague. The engineer had neither knowledge of it nor its prospect for the future."

One key failing was the lack of a leading truck, which would have reduced flange wear. Unlike South African efforts to improve Mallet and later Garratt articulated locomotives, Saito concludes, Japanese Mallets were "neither remodeled nor developed into a new design, and ended their lives in less than 20 years."

(The 0-4-4-0s mentioned above later received a leading axles and were reclassified as Class 9020 2-4-4-0s. The modification only marginally extended their working careers, which ended in 1925.)


Class 4600/9800 (Locobase 4419)

Data from narrowmind.railfan.net, which reproduces a plate from AE Durrant's The Mallet Locomotive. See also data from Record of Recent Construction #91 (Baldwin Locomotive Works, 1918), p.16-17; and DeGolyer, Volume 49, pp. 214+. Works numbers were 51946-51969.

Durrant's comment: "Baldwin's ...superheated Mallet for Japan did not inspire a general adoption of articulated power for the prevailing mountainous terrain." The photograph shows a surprisingly racy-looking design with relatively tall drivers outlined in white and a high-pitched boiler.

Baldwin noted that the locomotive was designed for grades as steep as 1 in 30 (3.3%) and curves as tight as 400 ft radius.

See Locobase 10974 (Alco's Mallet batch of 1912) for Akira Saito's May 2000 criticism of the original procurements of 0-6-6-0s from Baldwin (here), Henschel (Locobase 7622), and Alco (Locobase 10974).


Class 4600/9850 (Locobase 7622)

Data from Robert Garbe, "C+C Mallet-Heissdampf-Verbundlokmotive fur die japanishen Staatsbahnen" in Die Dampflokomotiven der Gegenwart (Berlin: Julius Springer, 1920), pp.513-515 (title translates, perhaps, to "Locomotives of Today".). See also the Kotsu Hakubutsukan Japanese transportation museum site [], last accessed 3 July 2006. Works numbers were 11657-11668 in 1912.

In Locobase 4419, Locobase reports on the Baldwin batch of Mallets delivered to Japan in 1912. This entry covers the Henschel order. All four cylinders used piston valves to supply steam.

These Mallets operated briefly on the Tokaido main line until the 9600-class 2-8-0s (Locobase 3816) replaced them. They were then relegated to branch-line service until the 1930s.

See Locobase 10974 (Alco's Mallet batch of 1912) for Akira Saito's May 2000 criticism of the original procurements of 0-6-6-0s from Baldwin (Locobase 4419), Henschel (here), and Alco (Locobase 10974).

Principal Dimensions by Steve Llanso of Sweat House Media

Class4600/97504600/98004600/9850
Locobase ID10974 4419 7622
RailroadImperial Government Railways (JGR)Imperial Government Railways (JGR)Imperial Government Railways (JGR)
CountryJapanJapanJapan
Whyte0-6-6-00-6-6-00-6-6-0
Number in Class241812
Road Numbers9750-97739800-98179850-9861
Gauge3'6"3'6"3'6"
Number Built241812
BuilderAlco-SchenectadyBaldwinHenschel & Sohn
Year191219121912
Valve GearWalschaertWalschaertHeusinger
Locomotive Length and Weight
Driver Wheelbase (ft / m) 8.83 / 2.699 / 2.749 / 2.74
Engine Wheelbase (ft / m)26.33 / 8.0326.17 / 7.9826.50 / 8.08
Ratio of driving wheelbase to overall engine wheelbase 0.34 0.34 0.34
Overall Wheelbase (engine & tender) (ft / m)47.92 / 14.6148 / 14.6347.92 / 14.61
Axle Loading (Maximum Weight per Axle) (lbs / kg)26,808 / 12,16026,544 / 12,04025,133 / 11,400
Weight on Drivers (lbs / kg)144,094 / 65,360142,650 / 64,705149,588 / 67,852
Engine Weight (lbs / kg)144,094 / 65,360142,650 / 64,705149,583 / 67,850
Tender Loaded Weight (lbs / kg)69,049 / 31,32062,350 / 28,28267,461 / 30,600
Total Engine and Tender Weight (lbs / kg)213,143 / 96,680205,000 / 92,987217,044 / 98,450
Tender Water Capacity (gals / ML)3240 / 12.273300 / 12.50
Tender Fuel Capacity (oil/coal) (gals/tons / Liters/MT)3 / 3 4.40 / 4
Minimum weight of rail (calculated) (lb/yd / kg/m)40 / 2040 / 2042 / 21
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)49 / 124549 / 124549 / 1245
Boiler Pressure (psi / kPa)200.20 / 13.80200 / 13.80203.10 / 14
High Pressure Cylinders (dia x stroke) (in / mm)15.51" x 24.02" / 394x61016" x 24" / 406x61016.54" x 24.02" / 420x610
Low Pressure Cylinders (dia x stroke) (in / mm)24.49" x 24.02" / 622x61025" x 24" / 635x61025.59" x 24.02" / 650x610
Tractive Effort (lbs / kg)28,645 / 12993.1730,244 / 13718.4632,659 / 14813.89
Factor of Adhesion (Weight on Drivers/Tractive Effort) 5.03 4.72 4.58
Heating Ability
Tubes (number - dia) (in / mm)101 - 2.25" / 57100 - 2.244" / 57
Flues (number - dia) (in / mm)16 - 5.5" / 14016 - 5.512" / 140
Flue/Tube length (ft / m)16.33 / 4.9816.24 / 4.95
Firebox Area (sq ft / m2)118.20 / 10.98122 / 11.34132.07 / 12.27
Grate Area (sq ft / m2)21.30 / 1.9821.20 / 1.9722.60 / 2.10
Evaporative Heating Surface (sq ft / m2)1414 / 131.361463 / 135.971457 / 135.37
Superheating Surface (sq ft / m2)286 / 26.57323 / 30.02404 / 37.50
Combined Heating Surface (sq ft / m2)1700 / 157.931786 / 165.991861 / 172.87
Evaporative Heating Surface/Cylinder Volume269.20261.95243.92
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation426442404590
Same as above plus superheater percentage498950035600
Same as above but substitute firebox area for grate area27,68628,79232,725
Power L1571759656674
Power MT524.82553.13590.17

All material Copyright © SteamLocomotive.com
Wes Barris