The Pennsylvania Railroad's class R1 comprised a single prototype electric locomotive constructed in 1934 by the Baldwin Locomotive Works of Philadelphia, Pennsylvania, US, with the electrical equipment by Westinghouse.

[2] It was built as a competitor to the GG1 design, but after trials the GG1 was selected for volume production on the basis of its superior tracking and riding qualities; the R1 prototype, however, remained in service.

[3] For many years, the R1's regular duties involved hauling the westbound Broadway Limited and returning eastward with a mail and express train.

The long rigid wheelbase of the locomotive caused occasional derailments in Sunnyside Yard and elsewhere.

Besides the R1, the PRR did not build or order any other 4-8-4 locomotives, however the T1 duplex was essentially a 4-8-4 with two sets of driving wheels as a 4-4-4-4.