The class was the first type in Japan to use the 4-6-4 "Hudson" wheel arrangement and was designed by Hideo Shima.

These nominal conversions were also seen as a way of bypassing the difficulties in obtaining approval from GHQ (General Headquarters, or Supreme Commander for the Allied Powers) for building completely new locomotives at the time.

The first eighteen locos delivered were allocated to Utsunomiya and Sendai depots to work express passenger duties on the Tōhoku Main Line.

With the spread of electrification together with the influx of C59s displaced from Tōkaidō Main Line duties, the C61s found themselves gradually pushed further north to Morioka and Aomori depots.

In later years, they were to be seen at the head of the newly inaugurated Hakutsuru limited express (between Sendai and Aomori) and the Hayabusa blue train (between Hakata and Kagoshima).