The HG 2/4 was a combined rack and adhesion locomotive of the meter-gauge Appenzell Tramway introduced in 1904. Since the HG 2/3 introduced in 1889 had a too complex Klose steering mechanism, the new locomotives were to be simpler in construction. The requirement was that they still could run the flatter sections in pure adhesion mode and engage the combined mode on the rack sections.

They were designed after the Winterthur system that combines the adhesion and rack drive with compound working. This meant that the high pressure cylinders were at the bottom and drove the wheels, while the low pressure cylinders at the top drove the crank axle for the rack drive. The crank axle worked onto the rack wheels via a 1 to 2,21 reduction gear, what meant that the low pressure cylinders moved at more than twice the speed of the high pressure cylinders, enabling all to be of the same size.

Numbers 5 and 6 were completed in 1904, followed by 7 and 8 in 1909 which were heavier. In adhesion mode they reached a top speed of 30 km/h. On the rack section, the maximum was 24 km/h when running uphill and 18 km/h when running downhill. In 1918, No. 6 was the only one to receive a superheater. Despite this it was one of the two which were retired first in 1931, while the others followed in 1932 and 1934-