The main automatic transmission to implement a torque converter (rather than a fluid coupling) was the Buick Dynaflow, which was introduced to the 1948 design year. In regular driving, the Dynaflow made use of only the major gear, depending on the torque multiplication on the torque convertor at reduced speeds. https://gearbox-auto39246.ampedpages.com/detailed-notes-on-gearbox-auto-60774957