At the beginning of the century, the Brünig line, the only narrow gauge line of the Swiss Federal Railways, needed new, more powerful locomotives for the adhesion section in the lower sections. While the previous locomotives only had three coupled axles, the new G 3/4 got an additional leading axle. Only numbers 201 and 202 were built in 1905. Six followed in 1912 and 1913, of which only the last one, No. 208, had a superheater from the start.

In the middle of the twenties, all others were superheated, too. After the top speed had been 45 km/h from the beginning, they were approved for 55 km/h in 1930 and for 60 km/h in 1936. After the Brünig line had been electrified in 1941 and 1942, they came to the Réduit, what was the Swiss system of fortifications and hidden gun positions.

After the war, three locomotives could be sold to the Thessalian railways in Greece. Two were scrapped already in 1947 and the rest got other tasks in Switzerland. 207 and 208 were the last ones to be retired in 1965. 208 was preserved as one of two SBB narrow gauge steam locomotives and was operational until it got damaged by a fire in 2013. In 2016 it came to the RhB shop at Landquart to be restored again.