Excerpt from Wikipedia:
The Challengers were named passenger trains on the Union Pacific Railroad and the Chicago and North Western Railway (which was replaced in 1955 by the Milwaukee Road). The economy service ran between Chicago, Illinois, and the West Coast of the United States. The trains had full Pullman service and coach seating and were an attempt to draw Depression-Era riders back to the rails. Food service was advertised as “three meals for under a dollar a day.”[1]
During the late 1930s the Challenger fleet was among the highest-patronized of American trains, and the best revenue producers of the UP passenger fleet.
In May 1936 the train commenced operation between Chicago and Los Angeles, California, on its own schedule. 1937 saw the UP partnering with the Southern Pacific Railroad to add a train from Chicago to Oakland, California, a line that would take the name San Francisco Challenger (the original then became the Los Angeles Challenger).
Discontinued in 1947, the Challenger name reappeared in 1954 on a streamliner. When Amtrak took over the nation’s passenger service in 1971, it ended the Challenger once and for all.[1]