A retractable thruster for a surface or submersible vessel, having thruster a propulsion assembly with a rigid structure secured to a cylindrical turbine. The rigid structure contains a motor suitable for rotating at lease one propeller inside the turbine via at least one rotary shaft positioned between the motor and the propeller. The thruster preferably further has a plate for closing the hull placed beneath the turbine and secured thereto, the propulsion assembly being displaceable between a retracted position in which it is at rest inside the hull and a deployed position for providing propulsion in which the propeller is immersed beneath the hull. The propulsion assembly is movable between the retracted and deployed positions by the propulsion assembly moving in a uniformly circular direction about an axis of rotation situated substantially no higher than the level of the hull.