As WWII was drawing to a close in 1945, the Reading Railroad examined their existing roster of motive power and realized they did not own any of the super-power steam locomotives that most other railroads owned and operated. The decision to obtain some of these locomotives was paramount, but with wartime restrictions still in place, the Reading had to look to their existing fleet for conversion. The I10-sa Class 2-10-0 locomotive fit the bill, and Reading started the in-house conversion of 30 of these I10 locomotives to the new class T-1 Northern.
The new T-1's entered service between 1945 and 1947 and were used primarily in fast freight service. Their operating territory included most of the Reading system, and they were also used in pool service with the Western Maryland Railway. The first 20 units were equipped for freight service. The last 10 were equipped for passenger service, but still primarily used for freight service.
