The Swiss Federal Railways had a highly electrified system during the Second World War, but retained little 0-6-0 tank engines for shunting. Due to war conditions coal was in short supply, but hydro-electricity remained plentiful. Therefore some of these small steam locomotives were converted to raise steam by electric heating. Power was taken at 15 kV, 16.6 Hz from overhead lines by a pantograph, and fed to resistance heating elements in the boiler, via two transformers rated together at 480 kW. Water feed was by normal steam injectors. These unique locomotives also retained the capability of being fired by coal in the usual way.