Brienz Rothorn Bahn rack-tank No 14, Brienz, 2003
As long ago as 1992, the Swiss locomotive manufacturer SLM delivered the first of a new class of modern oil-fired steam rack tank engines to operate on the the Brienz Rothorn Bahn rack-railway in Switzerland. The locomotives were designed by Roger Waller who based them on the existing fleet of locomotives, some of which had operated the railway since its construction in the late 19th century.
At the time, the railway owners had been considering converting entirely to diesel traction having successfully operated two such locomotives for a number of years, the diesels proving themselves superior in overall economy and in the number of passengers that they could haul up the 1700 metres that the line rises over its 7.6 km length (average gradient of 4%). The only disadvantage of the diesels was that visitors didn't like them, and preferred to ride on trains hauled by the line's ageing, expensive and increasingly unreliable steam locomotives.
Waller had little difficulty in convincing the railway that instead of replacing the old steam fleet, it should supplement it with new "modern steam" oil-fired locomotives. However he had much greater difficulty convincing his then employer, SLM, to take on the challenge of designing and building a new design of locomotive, and SLM only took on the work after Waller had undertaken a survey of Switzerland's mountain railways that indicated a potential market for at least 15 such machines. In fact, only 7 machines were built between 1992 and 1996 when SLM went out of business. Three went to the Brienz Rothorn Bahn in Switzerland and four to the Schafberg Railway in Austria.
The story of these remarkable locomotives, which exceeded their buyers' expectations, is told in a presentation that Roger Waller made to the (UK) Institution of Mechanical Engineers in 2003. A copy of this interesting and revealing paper can be downloaded by clicking here.