An actuator system comprising: an eye (50a, 50b) at each end, a cylinder running between the ends, and an actuator rod being slidably mounted within the cylinder, wherein a port is provided through the cylinder close to one end, through which fluid can be provided, wherein the actuator system further comprises: a rotatable lock mechanism provided at an end of the actuator rod and being fixed to move axially with the actuator rod, wherein one or more locking pins are mounted on and extended through the cylinder wall at a location between the fluid port and the opposite end of the cylinder, wherein the lock mechanism defines a path for the one or more locking pins, which has an entry passage through which the pin enters as the actuator rod extends, a guide surface along which the pin travels from the entry passage as the actuator rod retracts, a locking recess into which the pin is guided by the guide surface, and an exit passage into which the pin is guided as it is caused to leave the locking recess by extension of the actuator rod and subsequent retraction; and characterized in that a resilient detent finger is provided on the lock mechanism between the locking recess and the exit passage, which operates to block a return of the pin back into the locking recess after the pin has left the locking recess so as to prevent the pin from returning back into the locking recess when the actuator rod is extended to cause the pin to leave the locking recess. an eye (50a, 50b) at each end, a cylinder running between the ends, and an actuator rod being slidably mounted within the cylinder, wherein a port is provided through the cylinder close to one end, through which fluid can be provided, wherein the actuator system further comprises: a rotatable lock mechanism provided at an end of the actuator rod and being fixed to move axially with the actuator rod, wherein one or more locking pins are mounted on and extended through the cylinder wall at a location between the fluid port and the opposite end of the cylinder, wherein the lock mechanism defines a path for the one or more locking pins, which has an entry passage through which the pin enters as the actuator rod extends, a guide surface along which the pin travels from the entry passage as the actuator rod retracts, a locking recess into which the pin is guided by the guide surface, and an exit passage into which the pin is guided as it is caused to leave the locking recess by extension of the actuator rod and subsequent retraction; and characterized in that a resilient detent finger is provided on the lock mechanism between the locking recess and the exit passage, which operates to block a return of the pin back into the locking recess after the pin has left the locking recess so as to prevent the pin from returning back into the locking recess when the actuator rod is extended to cause the pin to leave the locking recess. a rotatable lock mechanism provided at an end of the actuator rod and being fixed to move axially with the actuator rod, wherein one or more locking pins are mounted on and extended through the cylinder wall at a location between the fluid port and the opposite end of the cylinder, wherein the lock mechanism defines a path for the one or more locking pins, which has an entry passage through which the pin enters as the actuator rod extends, a guide surface along which the pin travels from the entry passage as the actuator rod retracts, a locking recess into which the pin is guided by the guide surface, and an exit passage into which the pin is guided as it is caused to leave the locking recess by extension of the actuator rod and subsequent retraction; and characterized in that a resilient detent finger is provided on the lock mechanism between the locking recess and the exit passage, which operates to block a return of the pin back into the locking recess after the pin has left the locking recess so as to prevent the pin from returning back into the locking recess when the actuator rod is extended to cause the pin to leave the locking recess.