The class 01 of the Bulgarian State Railway was the first class in the Bulgarian standardization program. It was a Mikado express locomotive designed for mountainous lines. Like all these standard locomotives, it had many similarities to the German standard locomotives, but had a larger grate due to the lower quality coal available. Furthermore, the boiler was identical with the classes 02, 10 and 46. The 02 was the three-cylinder variant of the 01.

Between 1930 and 1935, 23 were built by manufacturers in Germany, Poland and Switzerland. Initially, they had numbers starting with 8000 and the new class scheme was only introduced in 1937. The Swiss locomotives were called “Tabakloks” since they were delivered in exchange for tobacco.

All 23 locomotives survived World War II. Around 1950, they were converted to run on mazut, what is a low-grade residue from oil production. All locomotives were retired from active service by 1979, with some stored as strategic reserve for some additional time.