The Stearman Model LT-1 (Light Transport) was a combination mail and passenger carrying transport that was developed for double duty from the basic M-2 "Speedmail" design. It was somewhat bigger and heavier and was powered with a Pratt & Whitney Hornet engine of 525 hp.

The forward fuselage which was fitted with cargo compartments on the M-2 was arranged into a cabin seating 4 passengers on the LT-1. The pilot still operated from an open cockpit in true "airmail fashion." It's ability to carry a payload of 1200 pounds, allowed for a load of 4 passengers with their baggage, and yet an additional 400 or 500 pounds of cargo.

Introduced early in 1929, the model LT-1 was initially developed for Interstate Air Lines which operated a route from Atlanta to Chicago, and to St. Louis, through Evansville, Indiana; a 1576 mile route. (C.A.M. #30). Interstate operated 3 of these aircraft and these were the only examples of this model that were built. The LT-1 served into the 1930's when Interstate was taken over by American Airways which is the forerunner of American Airlines today.