The Thoroughbred was a streamlined passenger train operated by the Chicago, Indianapolis and Louisville Railway (Monon) between Chicago, Illinois and Louisville, Kentucky via Monon, Indiana.

Following World War II new Monon president John W. Barriger III embarked on a program to renew the Monon's passenger service, long neglected.

The centerpiece of this program was a group of 28 surplus hospital cars originally built by the American Car and Foundry Company (ACF) in 1944–1945 for the U.S. Army.

[1]: 153 [2]: 23 The Thoroughbred made its first run on February 15, 1948, replacing the Day Express.

[2]: 23–28 The route length was 324 miles (521 km); the train operated as #5 (southbound) and #6 (northbound) and used Dearborn Station in Chicago.