The main automatic transmission to use a torque converter (rather than a fluid coupling) was the Buick Dynaflow, which was introduced for the 1948 model calendar year. In standard driving, the Dynaflow used only the top rated gear, relying on the torque multiplication on the torque convertor at lower speeds. https://sergiopadec.blogolize.com/the-smart-trick-of-gearbox-auto-that-nobody-is-discussing-73176903