The class 12, also called KuMoHa 12, is a collective name for similar electric railcars that were built between 1926 and 1941 for various areas of application. They were the first electric railcars used in Japan and operated on 1,500 volts DC. What they had in common was a length of around 17 meters, three passenger doors per side and benches arranged lengthways.

From the factory, the vehicles were power cars with one or two driver's cabs. With several conversions, the shape of many vehicles changed, so some temporarily lost the driver's cabs for use as powered trailers and got them back later. A total of 33 vehicles were transferred from the Japanese Government Railways to the Japanese National Railways in 1949. In 1987 the surviving vehicles went to JR East and JR Central where the last ones were retired in 1996 and 2002 respectively.