Soon after World War II began, it became apparent that the PRR would need a new locomotive to handle the surge in traffic due to the war effort. However with wartime restrictions on new locomotive designs imposed by the War Production Board the PRR was forced to borrow a design from another railroad. It chose the C&O's Class T\1 "Texas" type and the C&O loaned it a locomotive for evaluation. The PRR engineers prepared drawings based on the T1 and the Altoona Shops built what would become North America's largest fleet of "Texas" type locomotives.
The J1 and J1a locomotives spent the war years hauling freight on the railroad west of Altoona. Fifty five were assigned to the Central Region spread among the Western Pennsylvania Division-Pittsburgh Division, the Eastern Ohio Division-Eastern Division, the Eastern Ohio Divisions-Panhandle Division and the Lake Division-Cleveland Division. The other seventy were assigned to the Western Region spread among the Northwestern Division-Toledo Division, the Northwestern Division-Ft Wayne Division, the Northwestern Division-Logansport Division and the Southwestern Division-St. Louis Division
After the war they were displaced by diesels but the PRR found uses for them until they were retired in the late 1950s. Sadly like the C&O T1s, there are no surviving examples of the PRR's J1s.