The Electromotive Division (EMD) of General Motors (GM) Engineering Project Number 15990 completed the first model SD7 locomotive on 3, May 1951. This locomotive was painted in a vibrant EMD designed paint scheme, numbered (EMDX) 990, and went on a demonstration tour.
The Southern Pacific purchased this locomotive on 10. October 1952 (order P-1020) and was rebuilt by EMD (rebuild order 7512). It left EMD the next day after an extensive overhaul. Southern Pacific put the locomotive in service at Ogden, UT, 23. October 1952. It was numbered 5308, and became the sole unit in class DF-116 (DF standing for Diesel Freight).
There are a few things to note in this image. First, this locomotive retained it’s Leslie A-200 horns and winterization hatch. The locomotive has two 1,200 gal. tanks. The demonstrator had a steam generator, but according to Joseph Strapac’s Diesel Locomotive Compendium, Vol. 1, that was removed. Evidently the second (front) tank was used for fuel after the steam generator was removed. Let’s remember the standard fuel tank for an F3, F7, and later SD7s was also 1,200 gal, although some F7s were later equipped with 1,500 gal. fuel tanks. But that’s another story for another day.
Southern Pacific added the steam generator back at some point, and added the distinctive Mars signal light.
Another notable feature are the sill doors. As built, EMDX 990 (and sister locomotive EMDX 991) were built with smooth sill doors. Behind these sill doors were the electrical cables for the traction motors. Evidently, these got hot. EMDX 990 had her sill doors drilled for ventilation, while EMDX 991 (which eventually went to the Baltimore and Ohio railroad) did not. However, all production SD7s, as well as the follow-on SD9, SD18, and SD24 models, had ventilation louvers punched in the sill doors.
Note the “wings” on both ends – this locomotive was equipped with dual control stands for operation in either direction, although the short hood was the designated the front of the locomotive.