At the beginning of the 1890s, haulage of express trains on the Gotthard line was still separated. In the lowlands from Lucerne to Erstfeld the trains were hauled by light tank locomotives and in the mountains freight locomotives took over. In order to accelerate these trains, new locomotives were needed which combined sufficient tractive power with a higher maximum speed, thus making locomotive changes and double heading superfluous. The requirements were to move an express train of 140 tonnes on the mountain and 250 tonnes on the flat without assistance.
In order to enable sufficient tractive effort and, at the same time, good curve running, the locomotive was given three driving axles and a leading bogie, which made it the first locomotive of this wheel arrangement in Switzerland. A driving wheel diameter of 1,610 mm represented a good compromise for the required performance. For smoother running, coil springs were used instead of leaf springs, but were later replaced with leaf springs, too.
The first prototype with the number 201 was built with a three-cylinder compound engine. In order to develop a higher tractive force on the mountain, also the low-pressure cylinders could be supplied permanently with live steam. The 202 was a four-cylinder De Glehn compound, which also worked in compound on the mountain.
The 28 production locomotives were built with four cylinders because this allowed them to run more smoothly and more economical on the mountain line. Compared to the 202, the cylinders were enlarged while the boiler pressure was increased from 14 to 15 bars. The high-pressure cylinders acted on the first and the low-pressure cylinders on the second driving axle. A slightly smaller boiler was installed in the last six locomotives from number 225 onwards. These locomotives were later retrofitted with a superheater.
The locomotives could haul a 320-tonne express train on the flat at 50 km/h. A load of 140 tonnes was initially planned for the climb at 40 km/h, which was later reduced to 120 tonnes to reduce fuel consumption. Likewise, the tender was enlarged from a water capacity of 14.4 to 17 cubic metres. When the Gotthard Railway was nationalized in 1909, the SBB numbered the locomotives 901 to 930. After the line was electrified in 1920 and these locomotives were slower than later type A 3/5 locomotives, they were retired between 1923 and 1926.
