Locomotive Descriptions and Phases - EMD MP15 Series
The MP15 was introduced in 1974 as a replacement for the SW1500, initially combining most of the components of the SW1500 onto a 3-foot longer frame that provided room for GP "Blomberg" trucks. Like the SW1500, it was an end-cab design with a lowered hood and two conical exhaust stacks.
The "MP" in the model name referred to "Multi-Purpose" (as opposed to "SW" for "Switcher"). In combination with a larger fuel tank and an available toilet in the extra space near the cab, the new trucks qualified the MP15 for higher-speed road service for which the SW1500 was less suited. The remaining mechanical components were carried over, including a 12-cylinder Roots-blown 645-series engine generating 1,500 horsepower, an updated D32 main generator, four D77 DC traction motors, and an end-mounted belt-driven radiator fan.
The MP15 series was notable for having several dimensional changes and model variations, which has sometimes been a source of confusion in model-related discussions I've found. Below is a summary of the variations:
MP15, MP15DC
The MP15 was the first version, measuring 43' 6" over the end plates, 47' 8" over the coupler pulling faces, and 24' 2" between the truck centers. The proportions of the steps, pilots, and the ends of hood / underframe were the same as on the SW1500, with the extra 3' of length added to the hood immediately in front of the cab. The largest available fuel tank was increased from 1,100 gallons (5' 6" long) on the SW1500 to 1,400 gallons (7' long) on the MP15.
In early 1975 the pilot end plates were moved outboard by 6", widening the corner steps by the same amount and increasing the frame length over the end plates to 44' 6". However, the draft gear remained in the same location, so the overall length over the coupler pulling faces remained unchanged at 47' 8". This had the unusual effect of reducing the coupler-to-pilot distance from 25" to 19", rendering the coupler pockets nearly flush with the end plates and shortening the drop steps and uncoupling levers by 6". The reduced clearance was made possible at this point by absence of footboards, which previously required the additional space past the end plates.
A few months after the introduction of the MP15AC in early 1976, the draft gear was moved outward by 6", restoring the more typical 25" pilot-to-coupler distance and increasing the overall length to 48' 8". The truck centers and the cab and hood proportions remained the same throughout these changes.
Some time between the late 1970s and 1980, EMD changed the model name from MP15 to MP15DC. I haven't been able to confirm the exact date - a November 1975 parts catalog uses "MP15" everywhere except for using "MP15DC" on the title page; a March 1977 operator's manual uses "MP15"; a November 1980 service manual uses "MP15DC"; and a Southern Railway diagram book from 1980 uses "MP15" in the index and "MP15DC" in the diagram page to describe SOU 2348-2373, built in mid-1977. While the two model names are largely interchangeable, I've elected in the drawings to use "MP15DC" starting with Phase 3a units in 1976 to coincide with the change in overall length.
MP15AC
Up to this point, EMD switchers used a DC main generator and an end-mounted radiator fan. In late 1975, EMD introduced the MP15AC, which replaced the D32 generator with an AR10 main alternator, already in use on EMD road units. The radiators were changed to use side-mounted intakes (better suited to road service while running in reverse) and an electric radiator fan mounted horizontally inside the hood.
Since there was not enough room to mount the fan above the accessory rack near the end of the hood, the hood end was lengthened by 3' out from the engine compartment, along with a 6" length increase near the cab. The truck centers were increased by 6" to 24' 8", and the frame was lengthened by 18" to 46' 0" over the end plates and 49' 2" over the coupler pulling faces (using the same short 19" pilot-to-coupler distance as on the MP15 at the time). Since the underframe length increase was less than for the hood, the end of the hood occupied much of the front platform, requiring ladder-type steps in place of the previous angled steps. The cab remained in the same position relative to the rear end plate.
In 1976, the draft gear was moved outward by 6" as on the MP15DC, increasing the overall length to 50' 2".
MP15T
The MP15T appeared in 1984 and used a turbocharged 8-cylinger engine to produce the same 1,500 horsepower. While the underframe and many mechanical components were similar to the MP15AC, the hood was raised by 5.5", from 7' 2" to 7' 7.5" above the underframe (the first such increase since EMD's earliest 567-powered switchers). It had a single exhaust stack and larger radiators, a large inertial air intake near the cab on the left side (in place of louvered doors with filters) and a curved blower duct on the right side.
In contrast to the two earlier models which together sold 600 units, only 42 MP15T's were built - 41 for Seaboard System and a single DOWX unit - as overall US locomotive sales entered a slump in the early 1980s. By this point, there was relatively little separating EMD's end-cab switchers from mechanically similar GP units, especially with the GP15 series being produced concurrently (which had the added option of dynamic brakes). The MP15T would ultimately be the last of EMD's traditional end-cab switchers, as railroads increasingly began to use older road units such as the GP9 (and later the GP38 and even the SD40-2) for general-purpose switching and secondary service.
Dimension Summary
| Model | Length over coupler pulling faces | Length over end plates | Truck centers | Hood height above underframe |
|---|---|---|---|---|
| MP15 Phase 1 | 47' 8" | 43' 6" | 24' 2" | 7' 2" |
| MP15 Phase 2 | 44' 6" | |||
| MP15(DC) Phase 3 | 48' 8" | |||
| MP15AC Phase 1 | 49' 2" | 46' 0" | 24' 8" | |
| MP15AC Phase 2 | 50' 2" | |||
| MP15T | 7' 7.5" |
Phases
MP15, MP15DC
These phases are of my own making. I've elected to divide them according to the three variations in underframe and overall length.
| Phase | 1 | 2a | 2b | 2c | 3a | 3b | 3c1 | 3c2 | 3d |
|---|---|---|---|---|---|---|---|---|---|
| Dates | 1974-03 - 1975-03 | 1975-03 - 1975-07 | 1975-06 - 1975-08 | 1975-11 - 1976-01 | 1976-03 - 1976-12 | 1977-02 - 1977-06 | 1977-06 - 1977-10 | 1978-12 - 1979-11 | 1980-02 - 1983-01 |
| Underframe, steps | 43' 6" over end plates narrow steps | 44' 6" over end plates wider steps | |||||||
| Coupler to end plate | 25" | 19" | 25" | ||||||
| Overall length | 47' 8" | 48' 8" | |||||||
| Sand pipes under cab | Narrow spacing | Wider spacing | |||||||
| Cab roof front overhang | Long (12") | Short (4") | |||||||
| Brake vent valves | Attached to pipe segment branching off from main brake pipe | Spliced into main brake pipe | |||||||
| Coupler cut levers | Angled down toward coupler | Roughly horizontal, taller lifting pin on coupler | |||||||
| Door hinges | 2 | 3 | |||||||
| Hood air filter box | Flat top | Angled at rear | |||||||
| Left cab sub-base hinges | 4" Z-shaped | Blocks and pins | |||||||
| Exhaust | Two plain stacks | Silencer housing | |||||||
| Phase | 1 | 2a | 2b | 2c | 3a | 3b | 3c1 | 3c2 | 3d |
MP15AC
These phases are concurrent with phases 2c through 3d in MP15 / MP15DC production.
| Phase | 1 | 2a | 2b | 2c1 | 2c2 | 2d |
|---|---|---|---|---|---|---|
| Dates | 1975-08 - 1975-10 | 1976-01 - 1976-12 | 1977-03 - 1977-04 | 1977-10 - 1978-03 | 1978-07 - 1978-12 | 1980-10 - 1984-08 |
| Overall length | 49' 2" | 50' 2" | ||||
| Coupler to end plate | 19" | 25" | ||||
| Door hinges | 2 | 3 | ||||
| Hood air filter box | Flat top | Angled at rear | ||||
| Left cab sub-base hinges | 4" Z-shaped | Blocks and pins | ||||
| Exhaust | Two plain stacks | Silencer housing | ||||
Other Details
Handrails: The vast majority of MP15 units were built with full-length walkway-mounted handrails, but a few roads ordered units with hood-mounted handrails.
Hood air filter box: Not all units were built with the air filter box ahead of the cab. Those without it had a smooth sloped hood section similar to the SW1500.
Trucks: While all MP15 series units used "Blomberg" trucks, there were several variations in the castings (traded-in LFM frames vs. new Rockwell frames); brake / suspension design (leaf spring with clasp brakes vs. "Blomberg M" with single-shoe brakes); and wheel bearings (traded-in Hyatt bearings with angular housings, newer Hyatt bearings, or - on later units - Timken bearings with exposed end caps).
Sanding: Sand lines could be either dual or outboard-only. Many units were built with higher-capacity sand boxes, with angular housings extending from the hood under the radiators and raised square extensions on the sand boxes near the cab.
Draft gear: In addition to the variations in the position of the draft gear, units were built with either switcher-style draft gear common on the SW1500 (MS-485 or MS-488) or NC-390 draft gear with a beefer housing.
References
Electro-Motive Division. (1975). Replacement Parts Catalog No. 311, Switching Locomotives Model MP15DC - MP15AC.
Electro-Motive Division. (1976). Model MP15AC - 1500 hp Multi-Purpose Locomotive, Specification 8103.
Electro-Motive Division. (1984). Loco Outline, MP15T, Part no. 9565438. [Drawing].
Southern Railway. (1980). Diesel Electric Locomotive Diagrams - 1980. Retrieved November 2014 from http://southernmodeler.info/SRdiagrams.htm
Unofficial EMD Homepage. (2003). EMD MP15, MP15AC, MP15T Order Numbers. Retrieved June 2026 from https://trainweb.us/emdloco/mp15.htm