The Class DD51 (DD51形) is a B-2-B wheel arrangement diesel-hydraulic locomotive type operated in Japan since 1962. 649 locomotives were built between 1962 and 1978 by Kawasaki Sharyo, Hitachi, and Mitsubishi. The class was designed for mainline passenger and freight use with more power than the D51 and a higher maximum speed than the C62 steam locomotive classes. This was achieved by installing two 1,100 hp engines in an 18 metre long centre-cab design, unusual for mainline operation. The V12 DML61 engines were developed from the 6-cylinder inline DMF31 engines used in the Class DD13 locomotives.