One of the most interesting and least frequently used locomotive of SBB Historic is diesel locomotive Bm 4/4 II # 18451 from 1939, based at Olten. With three Leichststahlwagen (lightweight cars) it is running on a charter trip for english railfans between St.Margrethen and Rheineck. The locomotive was built, together with a sister locomotive, as Am 4/4 # 1001 and # 1002 by SLM, Brown Boveri Company and Sulzer for the SBB. The four-stroke, eight-cylinder Sulzer diesel engine with 880 kW power brought the very lightly-built locomotive (only 16 tons axle load) to a maximum speed of 110 km / h. In 1963, the two locomotives got new gearboxes, the top speed was reduced to 75 km/h, the tractive power increased. They were then labelled Bm 4/4 II # 18451 and # 18452. Locomotive # 18452 was scrapped in 1990, # 18451 is historic locomotive in Olten and its original Sulzer diesel engine from 1939 received a fully overhaul a few years ago.