There were nine HG 4/4 metre gauge Abt system cogwheel steam locomotives built by Schweizerische Lokomotiv und Maschinenfabrik (SLM) at Winterthur, Switzerland. They were produced starting in 1923 for the French Colonial Administration of French Indochina (today Vietnam) for use on a rack railway between Song Pha and Da Lat. The line was abandoned in 1970 due to the Vietnam War. Three engines were repatriated to Switzerland in 1990, one being returned for spare parts. At the time the locomotives were designed, SLM was able to draw on extensive experience in the construction of rack and pinion locomotives. The basis for the HG 4/4 was six HG 4/5 rack and pinion locomotive built in 1914 with the Winterthur drive system for the Nilgiri Railway in India. An additional four were delivered in 1920. However, the HG 4/4 power output was significantly increased and included a weight on drivers of 65 tons. An extremely clean DFB 704 is shown here during a test run near Realp - 23 Apr 2021 Georg Trüb.