A rotary actuator having a locking apparatus, the rotary actuator comprising: an outer housing comprising a cylindrical interior surface having a non-circumferential radial recess having at least one circumferential end formed therein; a rotor disposed within the outer housing and comprising; a cylindrical exterior surface rotatable within the cylindrical interior surface; an axial interior cavity; and a port disposed to be capable of rotational alignment with the non-circumferential radial recess and extending radially from the axial interior cavity to the cylindrical exterior surface; and, a piston disposed for axially reciprocal movement within the axial interior cavity of the rotor, the axially reciprocal movement being between a first position and a second position and comprising: a first portion having a first thickness; a second portion having a second thickness larger than the first thickness; and a piston bevel extending axially from the first portion to the second portion; and, a key disposed for radially reciprocal movement within the port and comprising: a radially proximal end having a first key bevel complementary to the piston bevel; and, a radially distal end; and a body extending from the radially proximal end to the radially distal end such that the radially proximal end contacts the second portion and the radially distal end extends into the non-circumferential radial recess when the piston is in the second position, and the radially proximal end contacts the first portion and the radially distal end does not extend into the non-circumferential radial recess when the piston is in the first position. an outer housing comprising a cylindrical interior surface having a non-circumferential radial recess having at least one circumferential end formed therein; a rotor disposed within the outer housing and comprising; a cylindrical exterior surface rotatable within the cylindrical interior surface; an axial interior cavity; and a port disposed to be capable of rotational alignment with the non-circumferential radial recess and extending radially from the axial interior cavity to the cylindrical exterior surface; and, a cylindrical exterior surface rotatable within the cylindrical interior surface; an axial interior cavity; and a port disposed to be capable of rotational alignment with the non-circumferential radial recess and extending radially from the axial interior cavity to the cylindrical exterior surface; and, a piston disposed for axially reciprocal movement within the axial interior cavity of the rotor, the axially reciprocal movement being between a first position and a second position and comprising: a first portion having a first thickness; a second portion having a second thickness larger than the first thickness; and a piston bevel extending axially from the first portion to the second portion; and, a first portion having a first thickness; a second portion having a second thickness larger than the first thickness; and a piston bevel extending axially from the first portion to the second portion; and, a key disposed for radially reciprocal movement within the port and comprising: a radially proximal end having a first key bevel complementary to the piston bevel; and, a radially distal end; and a body extending from the radially proximal end to the radially distal end such that the radially proximal end contacts the second portion and the radially distal end extends into the non-circumferential radial recess when the piston is in the second position, and the radially proximal end contacts the first portion and the radially distal end does not extend into the non-circumferential radial recess when the piston is in the first position. a radially proximal end having a first key bevel complementary to the piston bevel; and, a radially distal end; and a body extending from the radially proximal end to the radially distal end such that the radially proximal end contacts the second portion and the radially distal end extends into the non-circumferential radial recess when the piston is in the second position, and the radially proximal end contacts the first portion and the radially distal end does not extend into the non-circumferential radial recess when the piston is in the first position.