The present system provides a mechanism which provides mechanical locking of an apparatus, with fluid pressure-driven unlocking and an actuating force when an intended level of such pressure has been reached. The present system thus mechanically locks an apparatus against premature actuation caused by, for example, shock or vibration, until it is subjected to a level of pressure intended to actuate it. The present system is suitable for incorporation in any apparatus taking advantage of its ability to utilize fluid pressure to remove a mechanical block at an intended level of pressure and impart an actuating force.