Wikipedia
The M6 Presto-Matic was a Chrysler Corporation transmission produced from 1946–1953. It was a special manual transmission with a torque converter or fluid coupling. Although it had just two forward gears, an electric overdrive unit was attached and useful in either gear for a total of four forward speeds.
The driver would use the clutch pedal any time when selecting low, high, or reverse gear. Once underway, the accelerator could be eased and the car would engage the overdrive. With the Fluid Drive coupling, the car could be brought to a halt in gear without releasing the clutch and would creep like an automatic.
The Presto-Matic name was only used on Chrysler-brand cars. DeSoto called the transmission the Tip-Toe Shift, while Dodge used Gyro-Matic, Fluid-Matic, Fluidtorque, or Gyro-Torque. Chrysler and DeSoto sold the unit from 1946–1953, while Dodge did not introduce it until 1948. Plymouth introduced their Hy-Drive semi-automatic in 1953, but all were replaced by the PowerFlite automatic in 1954.