A compact operational retro-fit drive plant, for installation in the base of the bow or stern of various types of marine vehicle, in particular of displacement types, which serves for maneuvering and traveling at cruising speed on normal and particularly flat stretches of water. The drive plant includes a simple and economically produced water jet drive (1), having a propeller pump (8), for various types of engine and installations, which generates an efficient and completely controllable propeller thrust with optimized propeller approach flow and flat water capability. The propeller shaft (11) of the water jet drive (1) is arranged on the pressure side of the propeller pump (8) in a conventional 90 DEG elbow tube (6), the rotational axis (9) of the propeller is neither vertical nor horizontal, but has an inclination angle alpha of 20 DEG to 50 DEG, preferably between 25 DEG and 40 DEG relative to the baseplate (20) as a horizontal base. At the other end (14) of the elbow tube (6), which points downwards at an angle, an outlet housing section (7) is connected thereto and provided with a rotating base deflector array (16), in order to have control in all directions over the exit jet and thus the propeller thrust under the base of the water jet drive (1).