This masterpiece from SLM, cogwheel steam locomotive type HG 4/4 number DFB 704, was produced in nine copies from 1923 onwards for the French colonial administration of Indochina (now Vietnam) for use on the Lang Biang Cog Railway. Several remained operational until the end of the Vietnam War. Two HG 4/4s were returned to Switzerland in 1990. DFB 704 is now operational, as of 2022, DFB 708 continues to be rebuilt. In the 1920s when the locomotives were designed SLM had extensive experience in the construction of rack and pinion locomotives. The basis for the HG 4/4 type was the HG 4/5 rack and pinion locomotive with the "Winterthur Drive System". Six HG 4/5 engines in 1914, and four in 1920, were delivered to the Nilgiri Railway in India. The power output of the HG 4/4 was significantly increased. The design, with all weight on drivers, permitted the total weight of 65 tons to be applied for traction. In this photo 704 is on a warm-up run on adhesion trackage from Realp up the gorge of the Furkareuss - 23 Apr 2021 Georg Trüb.
 
Background image - On the last day of the 2020 season, 0-8-0T Class HG 4/4 number 704 pulls train 133 on the 11.8 percent rack section above Realp over the Furka pass to Oberwald. The temperature hovered around 0 degrees Celsius (32 F) as steam filled the air - 27 Sep 2020 Georg Trüb.