In order to make the leap to express locomotives with compound engines, the private state railway company had already built a single locomotive with a three-cylinder compound engine in 1897. This was known as number II 144 or class 25 and had a high-pressure cylinder with a diameter of 470 mm and two low-pressure cylinders with a diameter of 500 mm each. Since the compound principle did not prove its worth, the almost identical diameter of the cylinders was used and operated as a three-cylinder locomotive with simple steam expansion. Based on this experience, the decision was made to use a simple saturated two-cylinder locomotive when procuring the series machines until better solutions became available.
The 16 locomotives of this series were again delivered from the StEG's own workshops between 1900 and 1902 and classified as class 26. With a cylinder diameter of 490 mm, slower acceleration can be expected than with the prototype locomotive, but more powerful boilers were installed than with the contemporary kkStB 4-4-0 express locomotives. When the StEG was nationalized in 1909, these locomotives were assigned to the class 406 and the II 144 to the class 506. After the First World War, most of the examples went to Czechoslovakia. There, 14 of the class 406 became the 264.2 and one of the class 506 became the 264.301. After the Second World War, two of them ended up with MÁV in Hungary, where they became the class 227.