It seems to be a Swiss "C 5/6" called "Elefant". It was usually used for the Gotthard route. Swiss Railway changed very early (in the 50ies) to electrical engines, because Switzerland has no coal resources. My father was SBB engine driver and had to move this "Elefant" and the electrical "Krokodil". You see, in Switzerland those huge engines had names of wild and furious animals. We also had "Tigerli" and "Habersack" (the smaller ones).