Since the Reading Company was not allowed to build new locomotive types during World War II due to the War Production Board's regulations, existing locomotives had to be rebuilt. The class T-1 was created by rebuilding a total of 30 class I-10sa Consolidations to the 4-8-4 wheel arrangement. Among other things, the boiler with Wootten firebox were taken over and enlarged.

The first 20 locomotives were intended only for freight service and only had roller bearings on the carrying axles. Only in the last ten were roller bearings used on all axles in order to be suitable for possible use in front of passenger trains. In fact, they were rarely used in passenger service, but mostly in front of fast freight trains.

Their regular use initially ended in 1954. However, as traffic volumes increased, Reading used some of these machines again and also rented nine to the PRR. After these operations ended in 1957, the Reading ran a series of special trips with four locomotives that lasted until 1964 and became known as the "Iron Horse Rambles". The four locomotives used for this are all preserved today, of which only 2102 is operational.