The 1904 horseless-carriage gearbox often called the first true automatic was made by Sturtevant.
The Sturtevant gearbox was developed by the Sturtevant brothers in Massachusetts and fitted to the company’s early automobiles. It used centrifugal weights and clutches to change between forward ratios according to engine speed. As revs rose, the mechanism engaged the higher gear; as speed and engine revs fell, it shifted back to low.
This design is often described as the first true automatic transmission for a motor vehicle, but the wording needs context. It was an early automatic or semi-automatic mechanism rather than a modern hydraulic automatic. Abrupt gear changes placed heavy loads on its components, and reliability problems limited its practical success. The Sturtevant system therefore represents an important experiment, not the beginning of mass-market automatic driving.
The later General Motors Hydra-Matic, introduced for the 1940 model year, is generally credited as the first mass-produced fully automatic transmission. It used hydraulic controls and planetary gearsets, setting the pattern for the automatic gearboxes that followed. Sturtevant’s 1904 achievement came decades earlier, in the pioneering era of horseless carriages.