The "Zephyr"'s power (leading) car was numbered 9900, the baggage-coach combine car 505, and the coach-observation 570. The train was placed in regular service between Kansas City, Missouri, Omaha and Lincoln, Nebraska, on November 11, 1934, replacing a pair of steam locomotives and six heavyweight passenger cars, weighing up to eight times as much as the "Zephyr". By June 1935, it proved popular enough to add a fourth car, providing additional coach seating. The fourth car was originally a 40-seat coach number 525, but the following June it was switched to Twin Cities service, then back to the "Pioneer Zephyr" in December. Car 525 remained on the train until June 1938. Just over five years after it was introduced, the "Pioneer Zephyr" crossed the one million mile mark in regular service on December 29, 1939, near Council Bluffs, Iowa.