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 an order of 16 more of these locomotives was made, but they were built with radial trucks instead of the plate trucks the OG class M’s were equipped with. They are otherwise identical (but have considerably more tractive effort on curvy segments of the railroad.)

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 L2 motors have. 38 have been built for the Providence & Worcester, the Old Colony, and the Ontario Southwestern’s China Tunnel Railway project.

The last 8 of the initial M3 order (delivered in 2024) were high cab units for the western electrification which – at least from Binghamton west – has been cleared for high cube double stack containers (roughly 20'4" to top of container, 22'6" to contact wires)