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. It was numbered 4800 originally, swapped numbers with the victorious GG1 prototype to #4899, but was moved in May 1940 to #4999 to make room for the expanding GG1 fleet.^[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. The R1 suffered A catastrophic crash in 1951 with gg1 4800 slamming into it . both trains were traveling at 100 mph . nobody was hurt but the trains were badly damaged . all motors and electric parts were salvaged from the GG1 and the shell of the R1 was taken the two trains formed the rebuilt GG1 no 4800 . />

The R1 design had four driven axles in a rigid locomotive frame, like a steam locomotive. Each was driven by two 625-horsepower (466 kW) traction motors driving the wheels through a quill drive and sprung cups. Each end of the double-ended locomotive has a four-wheel truck to guide the locomotive at speed, giving the R1 a 4-8-4 wheel arrangement in the Whyte notation (AAR: 2-D-2; UIC: 2'Do2'). 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 2 sets of driving wheels, making it a 4-4-4-4. In many respects the design resembled the earlier, lighter P5, but with an extra driving axle and lower axle loads.