Diesel–electric railroad locomotion entered mainline service when the Burlington Railroad and Union Pacific used custom-built diesel "streamliners" to haul passengers, starting in late 1934. Burlington's "Zephyr" trainsets evolved from articulated three-car sets with 600 hp power cars in 1934 and early 1935, to the "Denver Zephyr" semi-articulated ten car trainsets pulled by cab-booster power sets introduced in late 1936. Union Pacific started diesel streamliner service between Chicago and Portland Oregon in June 1935, and in the following year would add Los Angeles and Oakland California, and Denver Colorado to the destinations of diesel streamliners out of Chicago. The Burlington and Union Pacific streamliners were built by the Budd Company and the Pullman-Standard Company, respectively, using the new Winton engines and power train systems designed by GM's Electro-Motive Corporation. EMC's experimental 1800 hp B-B locomotives of 1935 demonstrated the multiple-unit control systems used for the cab/booster sets and the twin-engine format used with the later "Zephyr" power units. Both of those features would be used in EMC's later production model locomotives. The lightweight diesel streamliners of the mid-1930s demonstrated the advantages of diesel for passenger service with breakthrough schedule times, but diesel locomotive power would not fully come of age until regular series production of mainline diesel locomotives commenced and it was shown suitable for full-size passenger and freight service.