The EMD SD24 is a 2,400 hp (1,800 kW) six-axle (C-C) diesel-electric locomotive built by General Motors' Electro-Motive Division of La Grange, Illinois between July 1958 and March 1963.

Power output of the SD24 was 33 percent higher than the 1,800 hp (1,340 kW) of the concurrent Roots blower-equipped SD18s with the same engine displacement.

[2] EMD thought the Duluth, Missabe & Iron Range Railway would want to start purchasing the SD24 and sent the first demonstrator to the DMIR painted in the road's livery.

In order to provide room for a larger fuel tank, the air reservoirs were relocated on the roof just behind the locomotive's cab.

[2] In addition, the extra maintenance requirements of the turbocharged engine were acceptable when they were some of the most powerful locomotives available, but in secondary service, they were an expensive way to get 2,400 hp (1,800 kW).

They later found work on shortlines such as the Chicago & Illinois Midland, the Wisconsin Southern (WSOR), the Iowa Interstate (IAIS), and the Indiana Harbor Belt.

[6] UP 423, however, was substantially rebuilt to UP 3100 in August 1968 with a constant-speed 16-645 3,000 hp (2,240 kW) prime mover, a new alternator and new traction motors.

With the constant-speed engine, speed control was via changing the level of excitation of the alternator; the traction motors were permanently wired in parallel.

From 1975, the locomotive was used as a heavy switcher at UP's North Platte, Nebraska hump yards, a fate common to UP's other surviving SD24s.

UP 414 did not receive as major a modification as #423, but it was refitted with a 16-645 engine, AR10 alternator and Dash Two electrical cabinet in May 1974, making it effectively an EMD SD40-2.

[5] Several high-nose Southern SD24s were rebuilt by the Milwaukee Road and Morrison Knudsen for Precision National's lease fleet in 1979.

Producing 1,800 horsepower (1,340 kW) (without the turbocharger), they were designated model SD18R - not to be confused with actual SD18 locomotives as manufactured by General Motors Electro-Motive Division.