JNR Class DD51

The JNR Class DD51 is a diesel-hydraulic locomotive operated by the Japanese National Railways and its various successors since 1962.
==History==
Designed to promote JNR's campaign of a "smokeless railway" to eliminate steam locomotives on the Japanese National Railways as part of their Power Modernization Plan, the DD51s were developed as a versatile freight locomotive for use on the Japanese rail network.
Largely replacing the older DF50 diesel-electric locomotives, which while well-received, had frequent reliability issues and were expensive, the DD51s were designed to haul as much as a D51 steam locomotive and as fast as a C62 steam locomotive, thanks to its twin engines. A total of 649 locomotives were manufactured from 1962 to 1978.
The DD51 remained the mainstay freight diesel locomotive for the JNR for many years. Replacements for the class were considered, such as the DD54 locomotives with a single higher-output engine as opposed to the DD51's two engines and the DE50 with reduced axle load; the unsatisfactory performance of the DD54 and the rapid introduction of electric locomotives diminishing any chance of mass-producing the DE50 meant that the DD51 remained the mainstay diesel locomotives of the JNR.
At their peak, the DD51s were used all over Japan with the exception of Shikoku. They replaced many highly popular steam locomotives, leading many enthusiasts to give them insulting nicknames such as "Red Pigs", "Paperweights" and "Dame Degoichi" (lit. "bad D51"). With the rapid progress of electrifying the Japanese rail network however the vast majority of DD51s were withdrawn by JNR's privatization and split, with the JR Group taking ownership of 259 locomotives, split between all constituents except JR Shikoku.
Under JR ownership, the locomotives are used to pull heavy freight trains and sleeper train services such as the Hokutosei. As of 2023, 15 locomotives are operational and seven have been preserved, including lead member DD51 1. A number of locomotives have been exported to other countries, such as Myanmar, Malaysia and Thailand.
==Design==
The DD51 featured a steeplecab-like design, giving it an appearance similar to that of a switcher locomotive; this design was chosen to help the locomotive reduce its weight by reducing its axle load.
==Specifications==
The DD51s are fitted with two V12 prime movers, designated the DML61, based on the DMF31S prime mover used on the earlier DD13 locomotives; this engine is turbocharged. Total power output is about 2,200 PS (1,600 kW). The DD51 uses a DW2A hydraulic transmission, being the first mass-produced diesel locomotive in Japan to use a hydraulic transmission; the transmission works similarly to a Voith turbo transmission and features three built-in torque converters. The engine cooling system is fitted with radiators on both sides, as well as an additional cooling fan. Coolant is circulated throughout the cooling system using a pump.
==Preservation==
The following Class DD51 locomotives have been preserved:
Number 	Manufacturer 	Date manufactured	Date retired 	Location 	Notes
DD51 1 	Hitachi 	31 March 1962 	31 March 1986 	Usui Pass Railway Heritage Park, Gunma, Japan 	Prototype locomotive, displayed outdoors
DD51 548 	Hitachi 	27 March 1967 	31 March 1986 	Mikasa Railway Memorial Hall, Mikasa, Hokkaido, Japan	Displayed outdoors; coupled to grain hopper HoKi 2341, ballast hopper HoKi 746 and caboose Yo 8006
DD51 610 	Mitsubishi Heavy Industries	22 May 1968 	31 March 1986 	Mikasa Railway Memorial Hall, Mikasa, Hokkaido, Japan	Displayed outdoors near various other diesel locomotives
DD51 615 	Mitsubishi Heavy Industries	20 July 1968 	31 March 1986 	Otaru City General Museum, Otaru, Hokkaido, Japan 	Displayed outdoors coupled to rescue car Oe 61 309; various parts missing
DD51 756 	Hitachi 	10 March 1972 	1 April 2010 	Kyoto Railway Museum, Kyoto, Japan 	Displayed indoors; underside of locomotive can be viewed
DD51 1040	Hitachi 	19 June 1973 	1 February 1994	Namikawa Railway Heritage Park, Kyoto, Japan 	Displayed outdoors near cab of 22-1003
DD51 1187	Hitachi 	1 July 1977 	1 April 2003 	Tsuyama Railroad Educational Museum, Okayama, Japan 	Displayed in roundhouse
The following Class DD51 locomotives were preserved in the past but have since been scrapped:
Number 	Manufacturer 	Date manufactured	Date retired 	Last location 	Notes
DD51 849 	Mitsubishi Heavy Industries	2 August 1972 	26 January 1987	Railway Technical Research Institute, Tokyo, Japan	Displayed outdoors; scrapped circa 2000s
DD51 865 	Mitsubishi Heavy Industries	13 March 1973 	31 March 1986 	Moji Rolling Stock Depot, Moji, Kyushu, Japan 	Scrapped at unknown date
DD51 872 	Mitsubishi Heavy Industries	31 July 1973 	20 January 1987	Moji Rolling Stock Depot, Moji, Kyushu, Japan 	Scrapped at unknown date
DD51 1037	Hitachi 	11 May 1973 	6 December 1999	JR Central Hamamatsu Works, Hamamatsu, Japan 	Painted in JR Freight paintscheme; scrapped at unknown date
==Gallery==
File:JNR DD51 756 2023.jpg
File:JNR DD51 1 2023.jpg
Category:JR Group trains
Category:B-2-B locomotives
Category:Diesel locomotives
Category:Diesel-hydraulic locomotives
Category:Hitachi locomotives
Category:Kawasaki locomotives
Category:Mitsubishi locomotives
Category:Japanese locomotives