The Aar Valley Railway between Wiesbaden and Langenschwalbach had a gradient of 3.33 percent, what posed problems for the 0-6-0 T 3 tank locomotives used there. They could only reach 16 km/h (10 mph) with five two-axle passenger cars. So new locomotives were ordered which could reach 20 km/h (12.5 mph) with seven cars on the same incline.
The new locomotives had a 0-6-2T wheel arrangement and 19 were built in Esslingen and by BMAG between 1892 and 1895. After World War I, two came to the Polish PKP and were designated TKi1. In Germany, only three were surviving when the new numbering plan of 1923 was created. They were to be designated class 901, but were retired in 1925 when the new numbers were to be applied. 