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May 2005 - Page 20


SD24

The First Turbo SD
by George Melvin

P art 7

UP SD24 402 is doing yard duty at East Los Angeles, CA, on April 18, 1982. Looking very good in the year of its retirement, it wears the 24 shield on the cab side and a smaller shield on the nose. Some of the red stripe on the sidesill has been removed. Note the yellow/gray color separation extends to the wind deflectors! The horn set is barely visible behind the winterization hatch on the long hood. Decals: Microscale 87-169.
Pete Coulombe photo, George Melvin collection

O

ur series on the SD24 concludes with the fleet operated by the Union Pacific (UP). This brings the story of the first turbocharged SD full circle, as the UP got the ball rolling in September 1955 with the installation of turbochargers in 19 GP9s for an in-service evaluation of the benefits that might be derived from this appliance. That experiment led to EMD building the first SD24 demonstrator in July 1958. The Union Pacific owned a total of 79 SD24s, making its fleet the second largest, falling a single unit behind the Santa Fe fleet of 80. To reach this number, the road bought 30 cab-equipped SD24s and 45 cabless booster variants (the only SD24Bs built) and bought all four demonstrator units when their demo tours were completed. The entire group of 75 units was built on one order with consecutive builders numbers; the A units were assigned builders numbers ahead of the B units. They were assembled between July and September 1959, behind the order for the Burlington, between the two orders for the Santa Fe and just ahead of the order for the Southern. Unlike the arrival of the model on the Burlington and Southern, they were not the biggest power on the Union Pacific when they arrived. The road had acquired a fleet of 25 4,500-hp General Electric gas turbines in 1952-54 and was receiving the 30 larger two-unit 8,500-hp Big Blow turbines between 1958 and 1961, while the SD24s fleet arrived. The comparison of the SD24 to the turbines may seem unfair, as the SD24 was the largest diesel on the UP when it arrived. The big engine trail that UP had trod since 1940 with the introduction of the Big Boy continued beyond the turbines to double-engined diesels from three different builders through the 1960s and into the early 1970s. The SD24s were numbered 400-429 for the A units and 400B-444B for the boosters. This was the next number series

above the GP9s that ended at 349. The cab units were the roads first low-nose units, while the B units were high-nose with a filler in the cab area with an access door and portal for light in each side. They were all equipped with the large fuel tank, dynamic brake and winterization hatches. The fleet dominated service over the Los Angeles & Salt Lake line between Los Angeles and Ogden, UT, and was commonly run with A units leading two to five booster units. They arrived in the then-current standard variation of the Armour Yellow and Harbor Mist Gray livery, with the roadname on the hood sides and nose of cab units. The Dependable Transportation slogan on the cab side was initiated on the SD24. Almost two years after the fleet was in service, the UP purchased the three units built in August 1960 as demonstrators in a failed attempt to land an order from the Southern Pacific. These units were the later style with the flared-top radiator fans and radiator grilles with two sections rather than four. These units, and the single Kennecott Copper unit featured last month, were the only late SD24s built. This trio was numbered 445-447 just above the last booster unit. Eleven months later, in July 1962, the first SD24 built became the last one purchased by the UP when the original demonstrator unit 5579, built in July 1958, became Union Pacific 448 at age four. It stood out as the only high-nose SD24 cab unit on the UP. It differed from production high-nose units built for the Burlington and the Southern in that the cab was the same height as the long hood, rather than being about a foot high on the regular production high-nose SD24s. Union Pacifics desire to upgrade and improve existing units manifested itself on two SD24s. Unit 423 was upgraded in 1968 with a 3,000-hp 645 prime mover and other features

20 MODEL RAILROADING

MAY 2005

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