The first automatic transmission to utilize a torque converter (as opposed to a fluid coupling) was the Buick Dynaflow, which was launched with the 1948 model yr. In standard driving, the Dynaflow applied just the top rated gear, depending on the torque multiplication with the torque convertor at decreased speeds. https://gearboxauto86307.pointblog.net/a-secret-weapon-for-gearbox-auto-77381155