In order to be able to connect their network to the network of China, Mantetsu had made the change from Cape gauge to standard gauge in 1906. Since the Japanese manufacturers couldn't deliver standard gauge locomotives within a short time, one turned to American manufacturers. The first four locomotives which were ordered came from ALCO and had originally been built for the Chicago Southern. These were 4-4-0 locomotives for regular passenger trains.

At the beginning, Mantetsu designated locomotives of this wheel arrangement as class A, and so they became A 50 to A 53. In the new scheme of 1920, they became the Amei class, what stood for their wheel arrangement that was also called “American” in the USA. Between 1927 and 1933, all four were rented to the private Sitao Railway. After their return to the state railway, they were usually used on secondary lines and sometimes with light trains on main lines. When they came to the China Railway in 1950, they became class AM1.