the Chicago, Burlington and Quincy Railroad, commonly known as the Burlington, had ordered two streamlined 10-car trainsets of its own: the Denver Zephyr, built by the Budd Company and modeled on the Pioneer Zephyr, the first articulated streamliner in the United States. While the City of Denver beat the Denver Zephyr into service, making its first run between Chicago and Denver on June 18, 1936, on May 31 the Burlington had deployed two of its existing trainsets, the original Zephyr and the Mark Twain Zephyr, on its own route between Chicago and Denver as the Advance Denver Zephyr. While as fast as the City of Denver, the three-car sets in no way compared to amenities aboard the 12-car Union Pacific streamliners, which included the "Frontier Shack" tavern, a dining-cocktail lounge, and a sleeper-lounge-observation car. The Burlington's new equipment would arrive in November. The two services operated on nearly-identical schedules. Fulfilling its early promise, the City of Denver traveled at an average speed of , the fastest of the Union Pacific's streamliners. The competition between the two trains remained unchanged for nearly twenty years. Even as it upgraded and replaced its other streamliners, Union Pacific kept the original trainsets on the route until 1953, finally introducing new lightweight equipment in 1953–1954. The following year, on October 30, 1955, the Chicago, Milwaukee, St. Paul and Pacific Railroad (the "Milwaukee Road") began handling the Union Pacific's streamliners east of Omaha, replacing the C&NW. The Burlington replaced the Denver Zephyr'''s equipment in 1956. With both trains sporting new equipment competition intensified. The Burlington included "Vista-Dome" dome cars on the Zephyr; within a year the Milwaukee Road's Super Domes began making appearances on the City of Denver. The Burlington also began operating a slumbercoach, an innovative economy sleeping car. Having none of its own, the Union Pacific leased two all-roomette Pennsylvania Railroad sleeping cars and billed it as "Slumbercoach service." Nevertheless, in the words of railroad historian Joe Welsh the Denver Zephyr "made mincemeat of the UP's City of Denver." Throughout the late 1950s and 1960s the Union Pacific gradually downgraded its passenger services and consolidated trains as losses mounted. The westbound City of Denver and City of Portland began joint operation in 1959. On September 7, 1969, the Union Pacific combined five of its Chicago–West Coast streamliners into a single massive train dubbed by critics the "City of Everywhere." This train included the City