As the name suggests, the S 1 was the first express (Schnellzug) locomotive that the Prussian State Railways had procured according to standardized design sheets. A distinction must be made between the first design with a compound engine from 1884 and the later simple production version from 1885.
The first variant mentioned was designated as the Hanover design and was the first express locomotive in Prussia to have a compound engine after the T 0 omnibus locomotive and the G 4.2 freight locomotive. Although it was only built 14 times between 1884 and 1887 due to the starting problems that had not yet been completely solved at the time, it formed the basis of the P 32. A design feature that distinguished the S 1 of the Hanover type from other 2-4-0 locomotives was the position of the cylinders. These were located between the leading and the first coupled axle, while they were usually arranged in front of the leading axle. This eliminated some of the overhanging moving masses, which improved smooth running.
The standard design, which was finally produced in large numbers from 1885 to 1898, again received a conventional engine with simple expansion, since the higher consumption was to be accepted in order to eliminate the starting difficulties. The cylinders were also arranged in front of the leading axle again, since the engines were intended for long, straight stretches. The development was based on the passenger locomotives of the classes P 2 and P 31. The use of larger coupled wheels, while not increasing top speed, did improve suitability for driving longer distances at high speed. For example, trains weighing 171 tonnes could be hauled continuously at 80 km/h on the Berlin-Hamburg route.
Both types were still used well into the 20th century, but since the advent of more powerful express trains they were increasingly used only in front of regular passenger trains. Most of the compound engines were decommissioned by 1914, and the last examples lasted until 1922. In the case of the standard design, most of the decommissioning took place towards the end of the First World War. However, four of them made it into the Reichsbahn's renumbering plan, where the numbers 12 7001 to 12 7004 were intended for them. Finally, they were no longer taken over, since the decommissioning took place until 1924.
