The very first automatic transmission to implement a torque converter (in place of a fluid coupling) was the Buick Dynaflow, which was released to the 1948 model yr. In typical driving, the Dynaflow used just the prime gear, counting on the torque multiplication in the torque convertor at reduced speeds. https://gearboxauto42951.fireblogz.com/65413408/rumored-buzz-on-gearbox-auto