These motors were built as B+(BF)+B (the center wheels are Fell wheels to engage the third rail) Fell incline motors to supplement and eventually replace the steam units on the (max 1 in 10) Mount Cube ramp.
The potbelly section of the motor contains the Fell wheels, which are fixed to the carbody; 4 600 HP motors (2 per set of wheels) drive them, while a set of hydraulic pistons are used to squeeze them against the fell rail while climbing or descending the ramp.
The end trucks were equipped with 200HP traction motors for operation off the rack; the idea was that the Fells could be used for assembling/disassembling trains for the trip over the incline, but ended up never being used for anything other than light moves in the staging yards at the ends of the Fell section.
After the incline was abandoned in 1947, #276 was rebuilt into a class 276 conventional(ish) motor for further operation on the Southern Vermont Traction Company’s line from Pownal, MA to Arlington, VT, and 274 & 275 were stricken from the roster and eventually scrapped.