All were tank locomotives, which did not have to be turned at terminal stations and could run in both directions at the same speed.

After the mid-1920s the more efficient Class N1 locomotives entered service and the Class I locomotives were transferred to the shunting duties.

456 was the first state railway locomotive to be fitted with a superheater; the results were successful and from then on, almost all the Finnish State Railways steam locomotives were fitted with superheaters.

489 was built in 1909, was equipped with a superheater, and was initially used for local traffic around Helsinki.

It served for 55 years before being withdrawn from shunting duties in 1964.