A hybrid drive system, comprising: a shaft; and an electrical machine, comprising: a stator; and a rotor attached to the shaft to rotate with the shaft relative to the stator; and an electromagnetic disconnect system configured to modify a position of the rotor to cause the rotor and the stator to be at least partially electromagnetically decoupled, wherein the electromagnetic disconnect system is configured to move the rotor relative to the stator to at least partially electromagnetically decouple the rotor and the stator, and wherein the electromagnetic disconnect system is configured to move at least a portion of the rotor axially along the shaft; and wherein the electromagnetic disconnect system includes at least one hydraulic actuator assembly configured to selectively move at least a portion of the rotor axially along the shaft to at least partially electromagnetically decouple the rotor and the stator; wherein the rotor includes a first portion and a second portion configured to move relative to each other between an electromagnetically coupled position and an at least partially electromagnetically decoupled position; wherein the first portion and second portion define at least one hydraulic cavity of the at least one hydraulic actuator assembly, and preferably wherein the at least one hydraulic cavity is a single annular cavity; and wherein the first portion and the second portion are slidably splined to the shaft via one or more mating splines on the shaft; and characterized by further comprising one or more backstops configured to limit motion and prevent separation of the first portion and the second portion in the at least partially electromagnetically decoupled position, such that the first portion and the second portion maintain a seal between them. a shaft; and an electrical machine, comprising: a stator; and a rotor attached to the shaft to rotate with the shaft relative to the stator; and a stator; and a rotor attached to the shaft to rotate with the shaft relative to the stator; and an electromagnetic disconnect system configured to modify a position of the rotor to cause the rotor and the stator to be at least partially electromagnetically decoupled, wherein the electromagnetic disconnect system is configured to move the rotor relative to the stator to at least partially electromagnetically decouple the rotor and the stator, and wherein the electromagnetic disconnect system is configured to move at least a portion of the rotor axially along the shaft; and wherein the electromagnetic disconnect system includes at least one hydraulic actuator assembly configured to selectively move at least a portion of the rotor axially along the shaft to at least partially electromagnetically decouple the rotor and the stator; wherein the rotor includes a first portion and a second portion configured to move relative to each other between an electromagnetically coupled position and an at least partially electromagnetically decoupled position; wherein the first portion and second portion define at least one hydraulic cavity of the at least one hydraulic actuator assembly, and preferably wherein the at least one hydraulic cavity is a single annular cavity; and wherein the first portion and the second portion are slidably splined to the shaft via one or more mating splines on the shaft; and characterized by further comprising one or more backstops configured to limit motion and prevent separation of the first portion and the second portion in the at least partially electromagnetically decoupled position, such that the first portion and the second portion maintain a seal between them.