Although surpassed in speed, power, and size by other locomotives, it is recognised as the most mass-manufactured locomotive in Japanese rail history. A total of 174 units are preserved in Japan, including five operational examples. An additional 13 are preserved in Russia and Taiwan, bringing the total number of preserved units to 187.
The classification consists of a "D" for the four sets of driving wheels and the class number 51 for tender locomotives that the numbers 50 through 99 were assigned to under the 1928 locomotive classification rule.
Following the Great Depression of 1929, Japan's rail freight demand declined. This delayed plans for the development and production of new freight locomotives, which were set to become successors to the Class D50. By the mid-1930s, economic recovery led to increased transport demand. Although electrification was in progress, steam locomotives remained the backbone of railway operations.[2] The result was the D51, a mechanically simple, versatile and fuel-efficient freight locomotive. The D51's chief designer, Hideo Shima, later described it as one of his most satisfying designs.[3]
Design
The D51 was based on the earlier Class D50, with which it shares many design fundamentals, such as a straight boiler and a 1D1 (2-8-2) wheel arrangement. Notable changes from the Class D50 included:[3][4]
Boiler Pressure and Traction Power: The boiler pressure was initially raised from 13 kg/cm² (D50) to 14 kg/cm² and later to 15 kg/cm² in wartime models. Despite a smaller cylinder diameter, these changes enhanced tractive effort.
Weight Reduction and Adaptability: Electric welding replaced traditional riveting, which resulted in reduction of axle load and overall weight. The maximum axle load was reduced from 14.99 t (D50) to 14.30 t, which enabled it to operate on lighter secondary lines, previously inaccessible to the D50.
Shorter Length: The D51 was 571 mm shorter than the D50 to fit on standard 60-foot (18.3 m) turntables common on branch lines, thus broadening its operational range.
Wheel Design: The D51 adopted box-spoked wheels, which distributed force more evenly across the wheel circumference.
Otherissues identified in the D50, such as derailments during reverse operations, were also addressed in the D51's design.[5]
Variants
The D51 is divided into three types based on the production period and design changes: early type, standard type, and wartime type.[3]
Early type (Namekuji)
D51 1
D51 23, one of the Super Slugs
Units produced: D51 1–85, 91–100
Period produced: 1936–1937
Early models are noted for their semi-streamlined appearance, with the feedwater heater positioned between the sand dome and chimney and enclosed in a long casing. This design earned the nickname "Slug" (ナメクジ, Namekuji). Two locomotives, D51 22 and 23, had an extended casing reaching the cab, referred to as "Super Slug" or "Big Slug." These were later modified to match other units because the extended casings required extra maintainance works. To balance the shortened overall length compared to the D50, the cab was made smaller. While this reduced weight, it also made the cab more confined, which some crews found uncomfortable. The weight of the first driving axle was lighter than the others, which caused wheel slip under heavy loads. The air-powered reverser was also found to be difficult to use due to its sensitivity. Later modifications, such as adding weight to the front deck, improved traction.[3][6]
Standard type
Units Produced: D51 86–90, 101–954
Period produced: 1937–1944
D51 260, one of the standard type D51s
The feedwater heater was relocated to a crosswise position in front of the chimney, and the suspension system was adjusted to improve axle weight distribution. The air-powered reverser was replaced with a manual version for better control. From D51 101 onwards, this updated design became standard, and most of the class was built to this specification. Wartime versions of these later units used simplified materials and construction methods, including wooden components and the omission of some design details to conserve resources.[3][6]
Wartime type
Units Produced: D51 1001–1161
Period produced: 1944–1945
D51 1105, built in 1944, with a boxy wartime-produced casing
Wartime models were built with substitute materials and reduced decorative elements. The dome was reshaped to a flat design, and wooden parts were used for components such as the smoke deflectors. Some tenders adopted a simpler 'ship-bottom' design. To increase hauling capacity, boiler pressure and axle load were raised, but the use of substandard materials and simpler welding caused reliability issues. This resulted in several boiler explosions, notably with D51 1140. After the war, many of these units were retrofitted with standard parts to improve safety and reliability.[3]
Operations
The D51 was widely used across Japan and was a common sight throughout the country. Primarily a freight locomotive, the D51 was occasionally assigned to passenger services, particularly on steeply graded lines such as the Chūō Main Line and the mountainous section of the Hakodate Main Line (Oshamambe–Otaru). On some flatter lines, such as the Uetsu Main Line, it also hauled passenger trains. Notable examples of its service include locomotives assigned to royal trains (on Emperor Shōwa's visit to Shimane in 1971)[7] and units used at yards on main lines, such as Shintsurumi and Suita, for hump shunting.
A D51-hauled freight train at Jōmon Pass on the Sekihoku Line
From the 1960s, D51 locomotives began to be retired as electrification and dieselisation progressed. However, many remained in service until the final years of steam operation in Japan. During the 1960s and 1970s, they were particularly prominent on steeply graded lines such as the Sekihoku Main Line, Tōhoku Main Line, Ōu Main Line, and Hakubi Line, often operating in double- or triple-headed configurations. These operations attracted railway enthusiasts, photographers, and media attention during the 'SL boom' period. While its ubiquity made the D51 an iconic machine, some enthusiasts seeking rarer locomotive classes expressed disappointment when encountering D51s.
The first D51s in Hokkaidō were assigned to the Otaru-Chikkō and Iwamizawa depots, with units such as D51 6 at Otaru-Chikkō and Nos. 48 and 126 at Iwamizawa. On the Nemuro Main Line, D51 locomotives assigned to the Shintoku depot were used on the old Karikachi Pass section without smoke deflectors and with limited installations of oil-fired systems.[8] D51 241 at the Oiwake depot hauled JNR' final steam-hauled train on 24 December 1975, on the Yūbari Line.[9]
Tōhoku
D51s were extensively used on major lines such as the Tōhoku Main Line, Ōu Main Line, Jōban Line, and Uetsu Main Line. On the Tōhoku Main Line, triple-heading operations were notable at Jūsanbongi Pass in Ichinohe, Iwate, with locomotives from Morioka, Ichinohe, and Shiriuchi depots. Similarly, triple-heading was common at Yatate Pass on the Ōu Main Line until 1971, by locomotives from depots such as Aomori, Hirosaki, and Akita.[10]
Kantō
In the Kantō region, D51s were assigned to depots including Takasaki, Utsunomiya, Mito, Ōmiya, Hachiōji, Tabata, Shintsurumi, and Shinkoiwa. At Mito, some units were fitted with automatic coal-feeding equipment in 1957 to accommodate the low-calorific coal from the Jōban coalfield. The electrification of lines such as the Sōbu Main Line and Takashima Line in 1970 led to the withdrawal of D51s from depots such as Shintsurumi.[11] D51 791 was used for farewell passenger services in October 1970, which operated between Tokyo and Yokohama.[12]
Chūbu
D51 698 at Nakatsugawa Depot
D51s were assigned to the Hokuriku Main Line, including depots at Tsuruga, Fukui, and Kanazawa, where they handled freight operations over steep passes such as the Yanagase and Yamano Tunnels. The electrification of the Hokuriku Main Line was completed by 1964, but some D51s remained in use for local and yard duties until 1971. On the Takayama Main Line, they replaced C58s and 9600s from 1959 until dieselisation in 1969.[13]
D51s operated on lines such as the Sanyō Main Line, Hakubi Line, and Mine Line. On the Hakubi Line, D51s based at Niimi depot were used for triple-headed limestone freight trains, which attracted significant attention from railway enthusiasts.[15]
Shikoku
Thirteen D51s were assigned to the Dosan Line, based at the Kōchi depot.These locomotives were eventually replaced by DF50 diesel locomotives by 1960.[16]
In Kyūshū, D51s were assigned to depots including Mojikō, Tosu, and Kumamoto. On the steeply graded Hisatsu Line, D51s replaced older locomotives such as the Class 4110 for services over the Yatake Pass. These locomotives were equipped with smoke collectors and oil-firing systems.[17]
According to the a journal published in 1956, ten locomotives were built by Nippon Sharyo for the Manila Railroad Company. These entered service in 1951. Numbered the 300 class, they were named after the cog locomotive class built in the 1910s for the Manila Railway. These locomotives differed from the rest of the D51 builds through the lack of smoke deflectors.[20]
The locomotives had a short service life in the Philippines as Manila Railroad ordered the dieselization of its entire network, having all steam locomotives retired by 1956.[21]
Taiwan Railways Administration DT650
From 1936 to 1944, Kawasaki, Kisha Seizō and Hitachi had built 32 D51s for Imperial Taiwan Railway. After World War II, they were taken over by Taiwan Railways Administration, and were classified DT650. In 1951, Kisha Seizō built three DT650s and Mitsubishi Heavy Industries built two DT650s for Taiwan Railways Administration.[22]
Preserved examples
Over 173 Class D51 locomotives are preserved in Japan.
The following is a list of preserved locomotives as of July 2023.[23]
Plinthed Russian D51-22 outside Yuzhno-Sakhalinsk Railway Station Sakhalin Island, Russia
Japan
Operational
D51 146: Operated on the Mooka Railway, runs on compressed air. (Semi-operational)
D51 200: Preserved in operational condition by JR West at the Kyoto Railway Museum, and was operating on Yamaguchi Line from November 2017 to May 2022, when a crack in one of its bogies was discovered. Restoration work and trial runs are continuing at the Railway Museum.
D51 320: Operated at a railway museum in Abira, Hokkaido on compressed air. (Semi-operational)
D51 498: Restored by JR East, based at Takasaki Rolling Stock Center, and pulls special-event trains on JR East lines.[24][25]
D51 827: Operated at Aridagawa Railway Park in Wakayama Prefecture, runs on compressed air.
Built in 1938 at the JNR Hamamatsu Works, locomotive number D51 200 has been overhauled and restored to operational condition for use as SL Yamaguchi and SL Kitabiwako starting in 2017.[26]
D51 1149: Preserved in Taga SL Park in Taga, Shiga
D51 200 at the Umekoji Steam Locomotive Museum in December 2011
D51 6 in Asahikawa, Hokkaido
D51 51 ("Slug" type)
D51 125 in Funabashi, Chiba
D51 170 in Hitoyoshi, Kumamoto
D51 222 in Yogi Park, Naha, Okinawa
D51 231 outside the National Museum of Nature and Science in Tokyo in December 2014
D51 286 in Otaru, Hokkaido
D51 452 at Ome Railway Park in Tokyo
D51 470 in Gifu
D51 745 in front of Minakami Station in October 2012
D51 774 next to the former Taisha Station in Izumo in March 2016
D51 792 in Kasugai, Aichi
D51 862 in Machida, Tokyo
D51 946 at the Coal and Fossils Museum in Iwaki, Fukushima
D51 1085 in Aridagawa, Wakayama
D51 1108 at Sendai Shinkansen Depot in July 2008
D51 1116 at The Hirosawa City in Chikusei, Ibaraki
In fiction
Hiro, a character based on the Class D51 and voiced by Togo Igawa, appears in the 2009 animated film Thomas & Friends: Hero of The Rails and thereafter became one of the show’s mainstays and the first character introduced after the change to CGI.
In the anime Hikarian the character Dozilas is based on the D51 498.
^JR西日本、D51形200号機が本線運転復活へ [JR West to restore D51 20 to mainline operational condition]. Mynavi News (in Japanese). Japan: Mynavi Corporation. 18 October 2014. Retrieved 21 October 2014.
^津山市 来月からD51の展示始まる [D51 to go on display at Tsuyama from next month]. RSK News (in Japanese). Japan: Sanyo Broadcasting Co., Ltd. 26 February 2015. Archived from the original on 26 February 2015. Retrieved 31 October 2015.
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