The Burlington "Zephyrs" were the first streamlined diesel-electric trains to serve the Twin Cities, and originally ran in an articulated configuration. The "400" (now renamed the "Twin Cities 400") followed in 1939, but using more conventional trucks and couplers to link passenger cars together. The "Hiawatha" had always been powered by a streamlined (or, in the terminology of the Milwaukee Road, "speedlined") steam locomotive. The "Twin Cities Zephyrs" added a second set of trains daily in 1936, running the "Morning Zephyr" and "Afternoon Zephyr" from each terminal. The "Hiawatha" added a second set of trains in 1939, and the "Morning Hiawatha" and "Afternoon Hiawatha" each provided daily service from Minneapolis-St. Paul and Chicago.