The 10 units (original numbers 7300-7309) were purchased for use as mainline power for Coast Line freights, and assigned to Taylor Roundhouse in Los Angeles for maintenance. They were renumbered 4000-4009 in the 1965 renumbering scheme. Not overly reliable, they were reassigned to local and yard service along with the RS-11s and RSD-12s as new units were purchased.

As mentioned, 4000-4005 were assigned to the Western Division. Bayshore Roundhouse was their maintenance point. 4004 was one of the test units that received a cabtop rotary beacon. They were mostly used on Peninsula locals, as their quick loading made them excellent commute train rescue units. They would remain in the area until transferred to Ogden during the great Alco purge from the Bay Area around 1975. All were subsequently sold to Chrome Crankshaft.

4006-4009 were assigned to the San Joaquin Division after their mainline days were over. Fresno was their maintenance point, but Tracy was a good place to see them. 4006 was rolled in a grade crossing collision, and rebuilt at the Sacramento shops after a lengthly out-of-service period. Around 1973 they were transferred to the Western Division and were used on Bay Area locals and yard jobs, most often as switchers in the Oakland Terminal. 4009 was briefly assigned to Richmond Transfer and used on the "Richmond Drag" (a transfer job running between the yard in Richmond and the yard in West Oakland) and on the "Plant Job" that switched the Chevron refinery and went out the Richmond Belt Line. It was, shall we say, somewhat less than a rousing success, as it had an on-going disagreement with poor track, plus the truck drop equalizers tended to snag the retarders on the hump. One of the units was also tried on some of the jobs working out of East Oakland and East Pleasanton, with equally poor results. After that, they were mostly confined to the West Oakland, Desert, Homestead and Passenger yards, or loaned out to the Peninsula. 4009 was transferred to Ogden with the 4000-4005, and met the same fate. 4006-4008 were transferred to Texas and mostly worked out of Houston and San Antonio. 4007 was the last of the class to see service, and wasn't retired until 1980.

The units were fairly popular with crews, having adequate power and fast loading. The main drawback when switching was the location of the air brake stand. It was directly in front of the engineer when he faced forward, making it difficult to reach when operating backwards.