Abstract: A safe/arm device has a rotor that aligns or misaligns a path for an explve. The rotor is aligned by the effects of a fluid pressure differential acting upon a piston of the device. This pressure differential causes the piston to translationally move and this movement is transmitted to the rotor by a shaft. The shaft fits within an axial bore defined by the rotor. This axial bore in turn defines a helical groove. A ball, partially recessed within a well defined by the shaft, rides within this helical groove. As the shaft is translationally driven within the axial bore, the helical groove of the rotor tracks the ball. Translational movement of the shaft is thereby converted to rotational movement of the rotor. As a safeguard, the shaft is split into two sections, one in engagement with the piston and the other in engagement with the rotor. By this arrangement, a predetermined amount of movement of the piston is required before this movement is transmitted to the rotor.