The Southern(SOU) Railway was the last of the four major buyers of the SD24. Like the Santa Fe and Burlington, they had a fleet of elderly FTs coming due for replacement. The company owned a total of 68 FTs spread among the Southern proper; the Cincinnati, New Orleans & Texas Pacific(CNO&TP) and New Orleans& Northeastern (NO&NE) —three of the five affiliates that comprised the Southern System. The SOU owned 48 units and the CNO&TP and NO&NE had 12 and eight units, respectively. Also like the other SD24 customers,the Southern was looking to make another improvement in operating efficiency. The remarkable improvement from steam power to the FT and other early freight diesels had now become the status quo.
The roster of FTs provided a total of 91,800 horse-power when built. These engines had dieselized the most rugged mainlines of the system, such as the famous “Rat Hole,” the CNO&TP from Cincinnati south through the mountains to Chattanooga. Now they were getting worn out, and the SD24 was called upon to meet the expectations of the proud and aggressive Southern, whose slogans were Southern Gives a Green Light to Innovation and Southern Serves the South; the latter implying that no other road served that region!
In October 1959, delivery began on an order for 48 SD24s. These would provide a total of 115,200 horsepower, about 20% more than the FT fleet did in 1941-45 with a 30% reduction in the number of units. The increase in the total number of traction motors was only 6%, but the difference in tractive effort was remarkable. A 2,700-hp A-B pair of FTs produced about 65,000 pounds of tractive effort while a single 2,400-hp SD24 produced 93,700, and this is what really mattered on the sawtooth profile of the Rat Hole.
Production began in October 1959, after the largest order for SD24s by the Union Pacific and between the two orders for the Santa Fe. The first 23 units were assigned numbers 2502-2524 on the Southern, numbered behind a pair of GP9s built in 1955. In November and December, the smallest group, four units for the NO&NE, was built and numbered 6950-6953. In December, 21 units started arriving assigned to the CNO&TP. They were numbered 6305-6325, behind five F-M Trainmasters numbered 6300-6304, which were also built in 1955. This group was finished by February 1960. The numbering reflected the roads practice of the era to assign locomotives in specific number blocks for each subsidiary. The CNO&TP diesels were all numbered between 6000 and 6538, and the NO&NE units were numbered between 6800-6953. This numbering continued to be in sequence with deliveries rather than by model type well past the time that other roads recognized different types of diesels were indeed different and thus numbered in series of similar models. The old mentality that all diesels were just diesels had waned.
The entire group of units went to work on the Rat Hole and the hilly Knoxville Bristol line, and dominated those routes for several years. They operated in sets of three to five units and were mixed with the five Trainmasters that were usually relegated booster status between a pair of the more modern SD24s. The units were all equipped with high short hoods and dynamic brakes, with the short hood being the designated front of the unit. Icicle breakers were attached to the cab roof to protect the five chime horns from ice accumulation in the Rat Holes many tunnels, and automatic train control shoes were fitted on one truck. Perhaps more notable, they were the first units delivered in the black and silver livery that replaced the green and silver applied on diesels since 1939.
The SD24 fleet was quickly judged to be up to their assigned task and prompted the road to order 100 SD35s in 1966. These were followed by SD45s and GE U30Cs in 1967. The influx of six-motor road switchers allowed the road to assign them to freights over most of the system, so SD24s were mixed with the newer SDs and roamed the system.
The small group of NO&NE units was assigned to another SOU entity, the Alabama Great Southern in 1970. A renumbering was done in the fall of 1972 as the road decided to group similar models together. The 21 units of the CNO&TP kept their original numbers, and the others were fitted around them. The first five of the SOU block, units 2502-2506 became units 6300-6304, replacing the five Trainmasters retired in 1965, and the remaining 18 numbered 2507-2524 were renumbered above the CNO&TP units, becoming 6326-6343. The four NO&NE (6950-6953) were assigned numbers 63446347 above the SOU block.
During the 1970s, repainted units received the SOU shield on the hood ends, giving them an added touch of class in their second decade of duty for the Southern. Units 2506, 2516 (before renumbering), 6308, 6309, 6321, 6323 and 6345 are known to have worn the shields. The computer check letter was also added after the road number on the cab, and the initials of the assignment road (other than Southern proper) was placed under the number. These initials are not always present and model detailing should be referenced to a specific unit for accuracy.
The increasing numbers of newer SD units and advancing age of the SD24 fleet came together in late 1977, and the entire fleet was retired and sold to Precision National Corp. (PNC) in January 1978. Still serviceable, these units formed a lease fleet. Six units were leased directly to South East Coal Company and were used to move coal over Louisville & Nashville rails (in full Southern livery) for about a year until SECX bought former Union Pacific GP20s from PNC. These units also saw service on the Burlington Northern and Milwaukee Road, some with PNC logos added to the SOU paint. Units 6322, 6326, 6335 and 6339 were scrapped by PNC. A rebuilding program saw 26 of them rebuilt by Morrison-Knudsen or Milwaukee Road to SD10 status with their turbocharger and dynamic braking removed. These units were repainted a medium green with PNC marking in yellow and renumbered into an 1800 series but keeping the last two digits of their most recent SOU number; thus SOU 6300 became PNC 1800. Many of these units went on to serve on the Chicago & Northwestern and other roads.
The Illinois Central Gulf bought the remaining 18 units that did not receive the PNC renumbering and together with some of the 1800s and units from the Union Pacific, created an SD20 fleet in their Paducah, KY, shops, home of the Paducah Geep. Next month, we will study these units and other secondary uses for the durable SD24.