The EMD MP15DC was a 1,500 hp (1,100 kW) switcher-type diesel locomotive model produced by General Motors' Electro-Motive Division between March 1974 and January 1983. 351 examples were built. A MP15AC
variant, with an AC drive, was also offered. Between August 1975 and
August 1984 246 MP15ACs were built, including 25 for export to Mexico, and four built in Canada. The MP15DC replaced the SW1500 in EMD's catalog, and is superficially very similar to the predecessor model, using the same engine (a V12 EMD 645-series powerplant) in a similar design of hood and bodywork. The primary difference is the MP15’s standard Blomberg B trucks.


Switchers up to the SW1500 had been restricted to AAR type A switcher or Flexicoil lightweight trucks, both with a 96 in (2,438 mm) wheelbase. In 1973 60 special order Mexico-only SW1504s were built on a slightly longer frame, allowing EMD’s standard Blomberg B trucks, with a 108 in (2,743 mm) wheelbase, to be used. In EMD's eyes (among others) this made the new locomotive a road switcher
rather than a pure switcher, since it was capable of transition and
road speeds up to 60 mph (97 km/h) or so. The new model MP15DC
designation thus meant Multi-Purpose locomotive, 1500 hp, DC generator. Originally the locomotive was simply designated the MP15; the arrival of the alternator/rectifier MP15AC in 1975 changed the name.


With the success of the MP15, there was a demand for a model with an advanced AC drive system. The MP15AC replaced the MP15DC’s DC generator with an alternator producing AC power which is converted to DC for the traction motors with a silicon rectifier.
The MP15AC is 1.5 ft (457 mm) longer than an MP15DC, the extra space
being needed for the rectifier equipment. The alternator-rectifier
combination is more reliable than a generator, and this equipment became
the standard for new diesel-electric locomotive designs.


The MP15AC is easily distinguished from the DC models. Instead of the
front-mounted radiator intake and belt-driven fan used on all previous
EMD switchers, these have intakes on the lower forward nose sides and
electric fans. Side intakes allowed the unit to take in cooler air, and
the electric fans improved a serious reliability issue found in its
earlier DC sisters.