In 1969, to face the fast growing traffic (especially ore shipping), the White Pass & Yukon seeked to increase its diesel roster. The railroad turned to Alco (American Locomotive Company), precisely to its Canadian subsidiary Montréal Locomotive Works (MLW). The locomotive manufacturer proposed its DL535E model, a 1200hp 6-axle diesel-electric engine, with narrow hoods and a single cab. These locomotives were related to the classical Alco RS (road switcher) and were equipped with a new and more powerful version of the same Alco prime mover used on the WP&YR GE class 90. Seven of these engines (#101 to 107) were delivered by MLW to the White Pass & Yukon in 1969. Unfortunately two of them were almost immediately destroyed by the terrible fire of the Skagway roundhouse. That incident prompted the railroad to order three more locomotives. These three engines (#108 to 110) were delivered in 1971 again by Montréal Locomotive Works (despite the demise of its parent company Alco in 1969). The eight surviving engines were used by the WP&YR until the abrupt end of its operations in 1982. Later in 1988, the railroad re-opened in summer only as a tourist railroad, but the GE diesels were found to be sufficient to run the trains, so the first five Alco of the class were sold to a Colombian narrow gauge railroad, the Societad Colombiana de Transporte Ferroviario (STF). Yet in 1999, because of high tourist demand, the White Pass & Yukon wished to retrieve its five engines exiled in Colombia and bought them back from STF. Four of the ex-Colombian Alco have been put back into service on the WP&YR.