Modern automated manual transmissions (AMT) have their roots and origins in older clutchless manual transmissions that began to appear on mass-production automobiles in the early-1930s and 1940s, prior to the introduction of hydraulic automatic transmissions. These systems were designed to reduce the amount of clutch or gear shifter usage required by the driver. These devices were intended to reduce the difficulty of operating conventional unsynchronised manual transmissions ("crash gearboxes") that were commonly used at the time, especially in stop-start driving. An early example of this transmission was introduced with the Hudson Commodore in 1942, called "Drive-Master". This unit was an early semi-automatic transmission, based on the design of a conventional manual transmission, which used a servo-controlled vacuum-operated clutch system, with three different gear shifting modes, at the touch of a button; manual shifting and manual clutch operation (fully-manual), manual shifting with automated clutch operation (semi-automatic), and automatic shifting with automatic clutch operation (fully-automatic). Another early example of this transmission system was introduced in the 1955 Citroën DS, which used a 4-speed "BVH" transmission. This semi-automatic transmission used an automated clutch, which was actuated using hydraulics. Gear selection also used hydraulics, however, the gear ratio needs to be manually selected by the driver. This system was nicknamed "Citro-Matic" in the U.S.