Louisville & Nashville E6 diesels
Electro-Motive's model E6, introduced in November 1939, was the first U.S. mass-production passenger diesel. Some 92 A units (like the Louisville & Nashville pair shown here) and 26 B units rolled out of the builder's La Grange, Ill., plant before wartime restrictions ended production in February 1939.
L&N photo, from Streamliner Pioneers 2005