The EMD GP15-1 is a 4-axle diesel-electric locomotive built by General Motors Electro-Motive Division between June 1976 and March 1982. Intended to provide an alternative to the rebuilding programs that many railroads were applying to their early road switchers, it is generally employed as a yardswitcher or light road switcher. This locomotive is powered by a 12-cylinderEMD 645E engine, which generates 1,500 hp (1,119 kW). The GP15-1 uses a 50-foot-9-inch (15.47 m) frame, has a wheelbase of 29 ft 9 in (9.07 m) and has a length over couplers of 54 ft 11 in (16.74 m). A total of 310 units were built for American railroads. A number of GP15-1s remain in service today for yard work and light road duty. The radiator section is similar to those found on the EMD SD40T-2 and EMD SD45T-2 "tunnel motors," leading some observers to incorrectly identify the units as such or as GP15Ts, and giving them the nickname "baby tunnel motors".
The Missouri Pacific Railroad purchased more units than the other three buyers combined. For spotting purposes, the MP models have a number of visually distinguishing features, though not all were applied consistently to the MP units:
The MP units have a grab iron ladder mounted on both sides of the long hood end;
MP's initial order of GP15-1s rode on Blomberg M trucks rather than the more common Blomberg B (all subsequent units were delivered with Blomberg B trucks) — and, while the standard Blomberg B truck carries two brake shoes per wheel, many MP units were equipped with only a single brake shoe per wheel;
#1555–#1574 were outfitted with the standard 81" nose, while the remaining units (all built in December 1976 or later) came with an 88" nose;