In the 4.75 mile long Hoosac Tunnel in Massachusetts, growing traffic volumes at the beginning of the century caused major problems for the operation with steam locomotives due to smoke and steam. So the Boston & Maine planned to use electric locomotives to pull trains with their steam locomotive through the tunnel. With the steam locomotive idling, it created much less smoke and steam. So they electrified the tunnel with 11.000 V AC at 25 Hz in 1910.

Five electric locomotives were ordered from Baldwin and Westinghouse and numbered 2501 to 2505. They were of conventional boxcab design and rode on two bogies consisting of two powered axles and a leading axle. Three got a gear ratio for freight service, while the two others got a faster ratio for passenger service. Just one year later they were renumbered 5000 to 5004. In 1917, two more were built which were the first to be retired in 1942 and 1945. After diesel locomotives took over, all were retired until 1947.