Abstract: A fin deployment system for a projectile positioned in a chamber, the fin deployment system including a non-rotatable hinge pin shaft, a fin member, and a unidirectional ratchet collar member. The non-rotatable hinge pin shaft, which is coupled to the shell, defines a helically-oriented pathway. The fin member has a fin lug that couples the fin member on the hinge pin shaft for simultaneous axial and rotational movement along the helically-oriented pathway to a deployed position at an aft region of the projectile. Such movement is induced at least partially by application of a centripetal load and aerodynamic load as the projectile rotates upon launch from a chamber. The unidirectional ratchet collar member is disposed on the hinge pin shaft for unidirectional axial movement and radial expansion induced by the simultaneous axial and rotational movement of the fin member that retains the fin member in the deployed position.