The Class C51 (C51形) is a type of 4-6-2 steam locomotive built by Kisha Seizo Mitsubishi and Japanese National Railways (JNR) Hamamatsu Works .

The C51 introduced 1.75 m (5 ft 9 in) diameter driving wheels to Japan.

In 1930, a C51 hauled the first Tsubame (swallow) express, reducing travel time between Tokyo and Kōbe to 9 hours.

[1] To alleviate a severe motive power shortage, sixteen JGR Class C51 locomotives, C51 8, 28, 30, 33 - 35, 88, 95, 96, 116, 130 - 132, 173, 175, and 178, all equipped with a Sumiyama feedwater heater, were converted to standard gauge and sent to the Central China Railway in 1939, where they operated primarily between Nanjing and Shanghai, at first with their original JGR numbers, later as パシナ (Pashina) class.

After the Liberation of China and the establishment of the People's Republic, these became China Railway class ㄆㄒ9 (PX9) in 1951, and reclassified as class SL9 (勝利9, Shènglì, "victory") in 1959.