the EMD SD24

Two SD24's lead this Santa Fe general merchandise train down Cajon Pass in 1959.  Santa Fe bought 80 of them.

The EMD SD24 was a 2,400 hp (1,800 kW) Co-Co diesel-electric built between July 1958 and March 1963. A total of 224 units were built for customers in the USA, comprising 179 cab-equipped A units and 45 cabless B units; the latter were built solely for the Union Pacific. The SD24 was the first EMD locomotive to be built with an EMD turbocharged diesel engine, sixteen months before the Bo-Bo type GP20. Power output was substantially higher than the 1,800 hp (1,350 kW) of the concurrent Roots blower-equipped SD18 with the same engine displacement.

The SD24 was only a moderate sales success and few had long service lives although a few rebuilds are still in operation, but the SD24 was a milestone in EMD locomotive development and the forerunner to today's high-powered six-axle locomotives.

Optional extras included multiple unit controls, a steam generator, dynamic brakes, winterization equipment, an air signal line, and hump control, but actually almost all delivered SD24s were very similar in configuration. The standard fuel tank offered a 1,200 US gallon capacity, while 2,400 or 3,000 US gallon tanks were optional. In practice, all SD24s ordered had the 3,000 gallon tank except for the last built, Kennecott Copper's single locomotive. In order to provide room for a larger fuel tank, the air reservoirs were relocated on the roof just behind the locomotive's cab. The tanks were known as "torpedo tubes" due to their long, thin design.

Winterization included a winterization hatch over one of the radiator fans, to direct warm air back into the engine compartment.

Either a low or high short hood could be ordered; in either case, the short hood was front by default. The Burlington Northern, Southern and first EMD demonstrator had high short hoods; the rest were low. Low short hoods from the factory had a pronounced downward slope of the top towards the nose, as did those of the contemporary GP20. Many of the high short hood units had their noses chopped later on, often as a consequence of rebuilding; these as a rule have flat-topped short hoods.  (edited from wikipedia)