The retractable azimuth thruster is an in-hull system that can operate in full azimuth thruster mode when deployed. It is used as an auxiliary propulsion system to increase the vessel’ s station-keeping capabilities. A tunnel can be incorporated in the design of the outer well so that the thruster can be used as bow thruster as well.
link:https://www.thrusterleader.net/retractable-azimuth-thruster1/