It was not until 1949 that the electric railway turned-off the overhead juice and embraced diesel technology; their first internal-combustion engine locomotive was a four-axle road switcher which arrived that year from American locomotive Co. In contrast to the company's standard light olive drab color scheme, the new 1500-hp RS2 (#700) from Alco wore a light yellow and green attire. It was not long afterward that ownership of the coal-hauling rail line was shifted to Union Electric Co. (of St. Louis), which already owned a pair of RS2s bought the year prior.

Lastly, industrial giant Peabody Coal Company outright purchased the strategic coal line in 1956; the small fleet of 244 V12-powered Alcos remained intact and went to work under the banner of newly created Peabody Short Line. By the close of 1961, the Schenectady-built trio were working for their third owner - Illinois Central - which had acquired the PSL property and equipment. Reportedly, one of the Alcos was patched briefly with a green diamond logo. It is thought that all of the four-axle Alcos eventually wore IC's black garb and sported the green logo.