The class M steeplecabs are another design for the D&H South electrification; B+B+B like 719, but with modern internals (& a slightly lower profile so it can fit through the ancient tunnels under Baltimore) so they can run under both the PV&T’s 3kvdc & the C&PD/NE Corridor’s 12.5vac.

These locomotives were actually designed before the class L, but weren’t ordered until the D&H got permission to string wire over Norfolk Southern’s just-acquired line from Sunbury to Harrisburg, so the first one came out of the Portland Shops in fall of 1999, after 799 was already running on D&H’s route from Harrisburg to Washington, DC.

In 2002, another 16 motors were ordered, but were built with upgraded electronics and were placed into class M2.

In 2023, the Portland Shops started producing a third version of the class; class M3, like the streamlined class K7, uses an updated version of the drivetrain that the class L motor has. 38 have been built for the Providence & Worcester, the Old Colony, and the Ontario Southwestern’s China Tunnel Railway project.