The Union Railroad was part of US Steel and was responsible for freight traffic between some of their plants and the main lines of several railroads in western Pennsylvania. The low speeds made it possible to achieve the largest possible adhesive weight without using a leading axle and without exceeding the length of the existing turntables. There was an additional booster on the first tender axle.

Since these locomotives were the only ones in North America with the 0-10-2 wheel arrangement, the name “Union” came about. The service at the Union Railroad ended in 1949 with the purchase of the first diesel locomotives. Nine of the ten locomotives were sold to the Duluth, Missabe and Iron Range, which also belonged to US Steel. They retired from service there between 1958 and 1961 and DM&IR number 604 is now on display in Greenville, Pennsylvania.