A drive mechanism (16, 116A, 116B, 116C) for an electric propulsion system (4, 104) that comprises an electric machine (18, 118A, 118B, 118C), in which the drive mechanism (16, 116A, 116B, 116C) comprises a drive shaft (10, 110) with a longitudinal axis A, an engagement means, and a disconnect mechanism; the engagement means comprises a drive shaft engagement element and an electric machine engagement element; wherein the drive shaft engagement element comprises a first and second shaft gear ring, and each shaft gear ring is supported on the drive shaft (10, 110); each shaft gear ring comprises a plurality of gear teeth which are circumferentially disposed around the drive shaft(10, 110), and the gear teeth extend radially outward from the drive shaft (10, 110); the gear teeth of the first shaft gear ring have an axial length L1; the first and second shaft gear rings are axially spaced from each other along the drive shaft by a distance L2; the electric machine engagement element comprises a first and second gear set; the first and second gear sets each comprise a plurality of gear teeth which are configured to mesh with the gear teeth of the first and second shaft gear rings respectively; the gear teeth of the first gear set have an axial length L3; the first and second gear sets are separated from each other by a length L4 in the axial direction, length L1 is less than length L4; length L3 is less than length L2; characterised in that the disconnect mechanism is configured to reversibly move one of at least part of the drive shaft engagement element and at least part of the electric machine engagement element relative to the other of the engagement elements in an axial direction between a first position and a second position; in which in the first position the gear teeth of the first shaft gear ring are meshed with the gear teeth of the first gear set and the gear teeth of the second shaft gear ring are meshed with the gear teeth of the second gear set, and in the second position the gear teeth of the first shaft gear ring are axially between the first and second gear sets and the gear teeth of the first shaft gear ring are not meshed with the gear teeth of the first or second gear sets. the drive mechanism (16, 116A, 116B, 116C) comprises a drive shaft (10, 110) with a longitudinal axis A, an engagement means, and a disconnect mechanism; the engagement means comprises a drive shaft engagement element and an electric machine engagement element; wherein the drive shaft engagement element comprises a first and second shaft gear ring, and each shaft gear ring is supported on the drive shaft (10, 110); each shaft gear ring comprises a plurality of gear teeth which are circumferentially disposed around the drive shaft(10, 110), and the gear teeth extend radially outward from the drive shaft (10, 110); the gear teeth of the first shaft gear ring have an axial length L1; the first and second shaft gear rings are axially spaced from each other along the drive shaft by a distance L2; the electric machine engagement element comprises a first and second gear set; the first and second gear sets each comprise a plurality of gear teeth which are configured to mesh with the gear teeth of the first and second shaft gear rings respectively; the gear teeth of the first gear set have an axial length L3; the first and second gear sets are separated from each other by a length L4 in the axial direction, length L1 is less than length L4; length L3 is less than length L2; characterised in that the disconnect mechanism is configured to reversibly move one of at least part of the drive shaft engagement element and at least part of the electric machine engagement element relative to the other of the engagement elements in an axial direction between a first position and a second position; in which in the first position the gear teeth of the first shaft gear ring are meshed with the gear teeth of the first gear set and the gear teeth of the second shaft gear ring are meshed with the gear teeth of the second gear set, and in the second position the gear teeth of the first shaft gear ring are axially between the first and second gear sets and the gear teeth of the first shaft gear ring are not meshed with the gear teeth of the first or second gear sets.