The A 18, later called S 5, was a 4-4-0 express locomotive that had been ordered when it became evident that the A 15 and A 16 (the later S 3) were not powerful enough for the growing demands. Like its predecessors it was a compound, but had four cylinders arranged after the de Glehn system. In large parts it was identical to the de Glehn variant of the Prussian S 5¹, but had changes in detail like a boiler pressure increased by one bar and a common cover for safety valves and whistle.

50 were built between 1902 and 1904 and only four followed in 1913. 34 had rifled Serve tubes, while the others had conventional ones. The locomotives were named after rivers and were used in light and medium express service with train weights up to 240 tonnes and usual speeds around 80 or 90 km/h. After World War I two remained in Germany and the others were used by the AL until 1937.