The very first automatic transmission to employ a torque converter (in place of a fluid coupling) was the Buick Dynaflow, which was introduced with the 1948 design year. In standard driving, the Dynaflow used just the leading gear, depending on the torque multiplication on the torque convertor at reduced speeds. https://gearbox-auto10741.tokka-blog.com/33910529/gearbox-auto-an-overview