For particularly heavy express trains on mountainous routes, two prototypes of the class 06 were built in 1939 as the only German steam locomotive with a 4-8-4 wheel arrangement. They got the boiler of the class 45 and streamlined cladding. As with the 45, the boiler with the overly long tubes caused problems. There were also occasional derailments in narrow switches. Due to the Second World War, there was no series production and after the end of the war, no revised machines were built due to a lack of demand.