The very first automatic transmission to use a torque converter (instead of a fluid coupling) was the Buick Dynaflow, which was introduced for that 1948 model calendar year. In normal driving, the Dynaflow used just the major gear, counting on the torque multiplication in the torque convertor at decreased speeds. https://gearboxauto74062.ampedpages.com/top-guidelines-of-gearbox-auto-61094582