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.

In 2026, the Portland Shops made yet another version of the class M motors; the M4 is a lower horsepower and lower profile M intended for use on lines that don’t have the clearance for double-stack container trains.

This design was made because the TSR had finished their slow electrification of the Guelph Junction Railway and needed a big steeplecab that they could run under the wire and be able to do transfer freights on the CPR (from Guelph to the CPR’s classification yard east of Toronto). The M4dac (the first M4s that came out of the Portland Shops) produce up 6600 HP, and are equipped with both trolley poles and pantographs to operate on the entire ORRC system (limited to 4000 HP when they’re running under the ORRC’s 1500vdc overhead, but capable of 6600 HP elsewhere.))

This order was followed up by a 22 unit order for the CV, P&W, and SLR, which are ac+3000vdc only, and can put out 7200 HP.