They were called F's, or covered wagons. For years they pulled every style of train, from the "Zephyrs" to the "Super Chiefs" to merchandise and local freights. Newer, bigger, more powerful locomotives made them obsolete. More than 7,600 were built by General Motors between 1939 and 1960. Of the thousands that were built, only a handful still exist today. The others were traded in or simply cut up for scrap.

The Southern Pacific Railroad owned over 770 of these workhorses at one time. For roughly two decades these Black Widows dominated the SP system and the Sierras. The 6378 and 6380 are two late model EMD F-7a locomotives, built for and delivered to the Southern Pacific in July, 1952. The locomotives saw service over the entire system and still retain their classic snow plow pilots from their days of battling the harsh winters in the Sierras.

The 28 units of class DF-8, numbered 6378-6405, were delivered in A-A sets with no B-units and all were painted in the classic “Black Widow” SP freight scheme, as they were purchased primarily for that service. The premier passenger trains in 1953 were well in the hands of E and PA diesels as well as the large stable of GS 4-8-4 Daylight locomotives. The F’s had proven they were superior to the E-units in some applications and as the steamers were retired, some F-units were given 60:17 (79 MPH) gearing and placed in the passenger pool. These A-units were built with boiler controls and steam lines while the B-units of the DF-4 (8086-8139) and DF-12 (8290-8303) class carried the steam generator and water tanks. These units were often found at the lead of the San Joaquin Daylight, Owl, Californian, Argonaut, Klamath, system mail trains and special movements like troop trains.

This class was delivered with Nathan M-5 chime air horns, nose lifting lugs and 1500-gallon fuel tanks for extended range. The dynamic brake fans were enlarged to 48” to dissipate 700 amperes, up from 600 amperes on the 36’ fan equipped F-7’s. Snow plow pilots were added by SP.

The SP Black Widow and Daylight paint schemes were time consuming to mask, as both used four different colors. During the 1958 recession, SP experimented with some simplified two-color schemes. A “Halloween” scheme of black and orange was tried on a couple dozen units, but it was not acceptable. The 6378 is acknowledged as being the first SP unit to be painted in new system standard Lark Grey/Scarlet Red scheme in July 1958. 6365, 6378, 6382 and several other units were originally lettered with the boxcar style gothic on the nose and flanks; it was then decided to return to the SP classic Railroad Roman as standard for locomotives. All F-units in the passenger pool were painted gray/red, but only around 20% of freight F-units were painted, most going to scrap in the delivered colors.

The 6378 and 6380 were part of a group traded to General Electric for new units in the late 1960's. Luckily GE did not scrap these units as was the fate of 1000's of others. GE resold a group of these units, including the 6478 and 6480, to the Salzberg Family who owned a number or shortline railroads. The units were originally sent to the Wellsville, Addison and Galeton Railroad (WAG) in Upstate New York where they became WAG 2100 and WAG 2000, respectively. In August 1969, the units were transferred to the Louisiana and North West Railroad (L&NW) and were renumbered 46 and 45, respectively.