Designed by JGR's cheaf mechanical engineer Hideo Shima, they were built by Kawasaki Heavy Industries Rolling Stock Company, Kisha Seizo, Hitachi, Nippon Sharyo, Mitsubishi Heavy Industries and JGR's factories from 1936 to 1945.

[3] 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] Otherissues identified in the D50, such as derailments during reverse operations, were also addressed in the D51's design.

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.

To increase hauling capacity, boiler pressure and axle load were raised, but the use of substandard materials and simpler welding caused reliability issues.

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.

While its ubiquity made the D51 an iconic machine, some enthusiasts seeking rarer locomotive classes expressed disappointment when encountering D51s.

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.

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] 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.

[12] 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.

On the Kansai Main Line, they operated in double-headed configurations to manage the steep gradients of the Kabuto Pass.

On the Hakubi Line, D51s based at Niimi depot were used for triple-headed limestone freight trains, which attracted significant attention from railway enthusiasts.

On the steeply graded Hisatsu Line, D51s replaced older locomotives such as the Class 4110 for services over the Yatake Pass.

[19] According to the a journal published in 1956, ten locomotives were built by Nippon Sharyo for the Manila Railroad Company.