The Imperial ran as train 39-40, was inaugurated in 1932 as a local train operating in Southern California with a consist of several coaches and Standard Pullmans between Los Angeles and Yuma. Eastbound #40 from Los Angeles would route off the Sunset main line at Niland traveling at night thru the fertile Imperial Valley. Traveling 102 miles thru Brawley, El Centro and Calexico, the Imperial skirted the inside border of Mexico before rejoining the Sunset Routes main line at Araz Junction in California, a few miles west of Yuma. At the beginning of WWII (1942) the Imperial was discontinued as non-essential war time traffic, however by 1946 it was reinstated as a secondary passenger train to Chicago operating on the Golden State Route with the Rock Island Railroad. By 1953 the Imperial cut 2 1/2 hours off its running time of 58 1/2 hours to Chicago by rerouting back onto the Sunset main line between Niland and Yuma. A local passenger was then used to met the Imperial at Niland to maintain passenger service to Calexico with several coaches and an 8 sect-5 DBR Pullman.
The Imperial had lost its name by 1958, only a Chair Car tailed behind the head end equipment of Baggage, RPO, and Railway Express cars. On #40, Sealed Mail Storage and REA Express cars from Los Angeles headed eastward with drops at Phoenix, Tucson, El Paso, Tucumcary, Nashville, Memphis and Oklahoma City, returning Mail and Express cars were picked up along the route by the westward #39. The SP Rider Coach turned at Memphis and headed back to Los Angeles. An average ten car train, the Imperial had collected an interesting mixture of head end cars from other railroads; REA-Baggage and Express Reefers from Great Northern, Illinois Central, Missouri Pacific,Texas & Pacific, Rock Island, New Haven, even an occasional PRR Car found its way west.
The Santa Fe had announced during mid-1964, plans for a new overnight piggyback service from Los Angeles to Phoenix. This jolting news prompted the Southern Pacific to to handle TOFC Forwarded Merchandise and Multi-Level Autoracks that would originate in the LA Shops Yard. Plans for two additional East and West trains running between El Paso and Los Angeles would have require 16 more diesel units for a existing power shortage on the Sunset Route. It was directed by management that Eastbound Autoracks and 60' TOFC cars to Phoenix will to be included in train 39-40 ahead of the Mail and Express cars.
Because Autoracks and TOFC cars lacked the necessary thru steam connections normally used for passenger car heating, two streamlined, smooth-sided Shasta Coaches (No. 2381 and 2390) would be equipped with Vapor Heaters. These two cars had been set up with a conductors desk.
The mail, #40 would pull out of the Los Angeles Union Passenger Terminal at 11:30 pm, crossing over the Los Angeles River eastbound on the Sunset Line and stop along side the LA Shops Yard (old Los Angeles Shops) that had been set up for TOFC handling. The power (set of F-Units) would then be cut off from the head-end for the Autoracks and TOFC cars set in from the Shops Yard to finish #39s Eastward consist. In 1966 the Southern Pacific petitioned the ICC to remove the Rider Coach, but this request was denied and by 1967 the railroads lost the US Mail contracts, #39-40 last run was August-18-1967.