A shaft interlock system (100; 200; 300; 400) comprising: an interlocking piston (40; 41; 45; 49) configured to translate a movable locking apparatus (50; 51; 52; 720) to interface with a fixed locking apparatus (60; 61; 62; 63) of a turbine shaft (70; 71; 72; 73); a main body (10; 11; 12; 13) wherein the interlocking piston (40; 41; 45; 49) is at least partially disposed; an extension actuator (20; 21; 22; 23) disposed in the main body (10; 11; 12; 13) and in mechanical communication with the interlocking piston (40; 41; 45; 49) configured to exert an extending force on the interlocking piston (40; 41; 45; 49) in a first direction; wherein the movable locking apparatus (50; 51; 52; 720) may engage the fixed locking apparatus (60; 61; 62; 63) to permit the fixed locking apparatus (60; 61; 62; 63) and the movable locking apparatus (50; 51; 52; 720) to slip in the axial rotation domain in a first direction of rotation and preventing the fixed locking apparatus (60; 61; 62; 63) and the movable locking apparatus (50; 51; 52; 720) from slipping in the axial rotation domain in a second direction of rotation; and a retraction actuator (30; 31; 34; 37) disposed in the main body (10; 11; 12; 13) and in mechanical communication with the interlocking piston (40; 41; 45; 49); characterised in that the retraction actuator (30; 31; 34; 37) is configured to exert a retracting force on the interlocking piston (40; 41; 45; 49) in a second direction, opposite the first direction; the interlocking piston (40; 41; 45; 49) is configured to retract in the second direction in response to the retracting force in the second direction being greater than the extending force in the first direction; and in that the retraction actuator (31; 34; 37) comprises an oil channel (32; 35; 38) configured to conduct oil into a cylinder (33; 36; 39) within the main body (11; 12; 13) and exert a hydraulic force on the interlocking piston (41; 45; 49), wherein the extension actuator (21; 22; 23) comprises a compressed helical spring. an interlocking piston (40; 41; 45; 49) configured to translate a movable locking apparatus (50; 51; 52; 720) to interface with a fixed locking apparatus (60; 61; 62; 63) of a turbine shaft (70; 71; 72; 73); a main body (10; 11; 12; 13) wherein the interlocking piston (40; 41; 45; 49) is at least partially disposed; an extension actuator (20; 21; 22; 23) disposed in the main body (10; 11; 12; 13) and in mechanical communication with the interlocking piston (40; 41; 45; 49) configured to exert an extending force on the interlocking piston (40; 41; 45; 49) in a first direction; wherein the movable locking apparatus (50; 51; 52; 720) may engage the fixed locking apparatus (60; 61; 62; 63) to permit the fixed locking apparatus (60; 61; 62; 63) and the movable locking apparatus (50; 51; 52; 720) to slip in the axial rotation domain in a first direction of rotation and preventing the fixed locking apparatus (60; 61; 62; 63) and the movable locking apparatus (50; 51; 52; 720) from slipping in the axial rotation domain in a second direction of rotation; and a retraction actuator (30; 31; 34; 37) disposed in the main body (10; 11; 12; 13) and in mechanical communication with the interlocking piston (40; 41; 45; 49); characterised in that the retraction actuator (30; 31; 34; 37) is configured to exert a retracting force on the interlocking piston (40; 41; 45; 49) in a second direction, opposite the first direction; the interlocking piston (40; 41; 45; 49) is configured to retract in the second direction in response to the retracting force in the second direction being greater than the extending force in the first direction; and in that the retraction actuator (31; 34; 37) comprises an oil channel (32; 35; 38) configured to conduct oil into a cylinder (33; 36; 39) within the main body (11; 12; 13) and exert a hydraulic force on the interlocking piston (41; 45; 49), wherein the extension actuator (21; 22; 23) comprises a compressed helical spring.