In one aspect, a submarine with a boat hull and a propulsion drive for the submarine the propulsion drive is arranged outside the boat hull and comprises a housing and a first electric motor, with the housing embodying a channel for a flow of water through the channel in a main direction of flow from an inlet to an outlet of the channel, and with the first electric motor featuring a rotor which is arranged in the channel and is supported rotatably around an axis of rotation in the housing, with the rotor being embodied in the shape of a ring with a ring inner side and a ring outer side, and with blades for propelling the submarine being arranged on the ring inner side of the rotor.