The He 2/2 designates a family of two-axle rack-only locomotives which were built between 1897 and 1957. Since they came to a variety of operators, they were built in gauges of 800, 1,000 and 1,435 mm and were supplied either by DC or three-phase AC. The mechanical part of all locomotives was built by SLM, but the electrical part came from different suppliers. Their body varied in length and some were used as Rowan trains where a semitruck-like trailer was supported by the locomotive. All had two traction motors, but with varying output between 67 and 166 kW per motor. In total, 65 were built.

The first one was built for the Jungfrau Railway, followed by eleven others for this customer. They had a length of 4.38 to 4.52 metres, a weight of 14 to 17 tonnes and a total power of 162 or 184 kW. The Gornergrat railway was also one of the first customers and received four 134 kW locomotives in 1898 which were used for Rowan trains. The Wengernalp Railway was another large customer with 14 locomotives which were considerably longer at 5.74 metres. They had either 220 or 236 kW. The Trieste-Opicina rack railway used a variant with 294 kW on their tram network. An even more powerful variant was used by the Rigi Railway that had an output of 331 kW and was 6.13 metres long.