Abstract: The disclosure describes a hydraulic power transmission comprising a torque converter of which a pump impeller is adapted to be connected to an output shaft of an engine; a fluid coupling of the pump impeller is adapted to be connected to the output shaft of the engine; an intermediate shaft is connected to a turbine runner of the torque converter; an output shaft is connected to a turbine runner of the fluid coupling; a one-way clutch connects the intermediate shaft to the output shaft and is operable to transmit the torque only fron the intermediate shaft to the output shaft; and a control mechanism for controlling the fluid coupling to operate only when the rotation speed of the output shaft exceeds a predetermined value.