A linear actuator comprising: a screw including a first end portion and a second end portion, the second end portion including a cylindrical shaft portion that defines a longitudinal screw axis, the second end portion having an external thread; a nut coaxially arranged on the second end portion having an inner aperture having an internal thread mated with the external thread of the second end portion, the nut configured to axially translate along the second end portion from a retracted position to an extended position; a torque transmitting screw drive member that is configured to transmit torque to the screw and drive the rotation of the screw about the longitudinal screw axis; and a mechanical nut locking system configured to automatically lock the nut when the nut is retracted, wherein the mechanical nut locking system automatically disengages the mechanical lock when the torque transmitting screw drive member transmits torque to the screw in a direction that extends the nut, characterized in that the first end portion of the screw defines a cylindrical cavity concentric about the longitudinal screw axis, wherein the second end portion of the screw defines a cylindrical shaft portion concentric about the longitudinal screw axis; a first end portion of the nut defines a cylindrical nut cavity that is configured to receive a portion of the first end portion of the screw, the nut cavity including an inwardly radially extending retaining lip; and in that the linear actuator further comprises: a locking member extending through a portion of the first end portion of the screw and configured to catch on the retaining lip of the nut cavity when in a first position; and a sliding drive gear including a gear interface at a first end and a locking member interface at a second end, wherein the sliding drive gear is configured to extend and retract axially and thereby radially bias the locking member into engagement with the retaining lip of the nut cavity; wherein initial rotation of the sliding drive gear in a first direction translates the sliding drive gear axially without rotating the screw and subsequent rotation of the sliding drive gear in the first direction rotates the screw and thereby drives axial motion of the nut. a screw including a first end portion and a second end portion, the second end portion including a cylindrical shaft portion that defines a longitudinal screw axis, the second end portion having an external thread; a nut coaxially arranged on the second end portion having an inner aperture having an internal thread mated with the external thread of the second end portion, the nut configured to axially translate along the second end portion from a retracted position to an extended position; a torque transmitting screw drive member that is configured to transmit torque to the screw and drive the rotation of the screw about the longitudinal screw axis; and a mechanical nut locking system configured to automatically lock the nut when the nut is retracted, wherein the mechanical nut locking system automatically disengages the mechanical lock when the torque transmitting screw drive member transmits torque to the screw in a direction that extends the nut, characterized in that the first end portion of the screw defines a cylindrical cavity concentric about the longitudinal screw axis, wherein the second end portion of the screw defines a cylindrical shaft portion concentric about the longitudinal screw axis; a first end portion of the nut defines a cylindrical nut cavity that is configured to receive a portion of the first end portion of the screw, the nut cavity including an inwardly radially extending retaining lip; and in that the linear actuator further comprises: a locking member extending through a portion of the first end portion of the screw and configured to catch on the retaining lip of the nut cavity when in a first position; and a sliding drive gear including a gear interface at a first end and a locking member interface at a second end, wherein the sliding drive gear is configured to extend and retract axially and thereby radially bias the locking member into engagement with the retaining lip of the nut cavity; wherein initial rotation of the sliding drive gear in a first direction translates the sliding drive gear axially without rotating the screw and subsequent rotation of the sliding drive gear in the first direction rotates the screw and thereby drives axial motion of the nut. a locking member extending through a portion of the first end portion of the screw and configured to catch on the retaining lip of the nut cavity when in a first position; and a sliding drive gear including a gear interface at a first end and a locking member interface at a second end, wherein the sliding drive gear is configured to extend and retract axially and thereby radially bias the locking member into engagement with the retaining lip of the nut cavity; wherein initial rotation of the sliding drive gear in a first direction translates the sliding drive gear axially without rotating the screw and subsequent rotation of the sliding drive gear in the first direction rotates the screw and thereby drives axial motion of the nut.