An axial piston pump having: a fluid inlet, and a fluid outlet; a rotatable, one-piece piston housing (204a; 204b) carrying one or more pistons movable within one or more respective sleeves formed by the piston housing, a circumferential row of fixed field members (501a; 501b; 701; 803) being mounted to the piston housing at a mounting location formed by the piston housing, the mounting location being radially outward of the one or more sleeves a stator (503; 704; 802) surrounding the piston housing (204a; 204b) and including a circumferential row of armature windings such that the piston housing and the stator form an electro-magnetic motor operable to rotate the piston housing; and a swashplate engaged with the one or more pistons such that rotation of the piston housing relative to the swash plate around an axis of rotation produces reciprocating movement of the one or more pistons for the pressurisation of fluid received into the one or more sleeves from the fluid inlet and then discharged from the one or more sleeves to the fluid outlet; characterised in that the fixed-field members (501a; 501b; 701; 803) and the armature windings are configured such that, when an electrical current is passed through the armature windings, the armature windings generate a magnetic field which interacts with a magnetic field generated by the fixed-field members, the interaction providing a force which urges the piston housing in an axial direction to counteract a hydrodynamic force produced at the sliding interface between the one-piece piston housing and static parts of the pump, the magnitude of the force provided by the interaction being a function of the speed at which the piston housing (204a; 204b) is rotated. a fluid inlet, and a fluid outlet; a rotatable, one-piece piston housing (204a; 204b) carrying one or more pistons movable within one or more respective sleeves formed by the piston housing, a circumferential row of fixed field members (501a; 501b; 701; 803) being mounted to the piston housing at a mounting location formed by the piston housing, the mounting location being radially outward of the one or more sleeves a stator (503; 704; 802) surrounding the piston housing (204a; 204b) and including a circumferential row of armature windings such that the piston housing and the stator form an electro-magnetic motor operable to rotate the piston housing; and a swashplate engaged with the one or more pistons such that rotation of the piston housing relative to the swash plate around an axis of rotation produces reciprocating movement of the one or more pistons for the pressurisation of fluid received into the one or more sleeves from the fluid inlet and then discharged from the one or more sleeves to the fluid outlet; characterised in that the fixed-field members (501a; 501b; 701; 803) and the armature windings are configured such that, when an electrical current is passed through the armature windings, the armature windings generate a magnetic field which interacts with a magnetic field generated by the fixed-field members, the interaction providing a force which urges the piston housing in an axial direction to counteract a hydrodynamic force produced at the sliding interface between the one-piece piston housing and static parts of the pump, the magnitude of the force provided by the interaction being a function of the speed at which the piston housing (204a; 204b) is rotated.