trains 9900 and 9903. This new service was known as the Advance Denver Zephyr and operated on a 16-hour schedule. The trains did not have sleepers, but introduced hostesses called "Zephyrettes".

In the meantime, after the success of the 3-car and 4-car Pioneer Zephyr, Twin Zephyrs, and Mark Twain Zephyrs, the Burlington had ordered two pairs of longer stainless steel streamliners from the Budd Company. One pair