It is known to use springs to deploy steering fins on board projectiles, each fin having its own spring and a separate mechanism for latching it in its deployed position. Described herein is an integral spring/latching mechanism (4) which is operable to deploy a plurality of fins and then to latch them in their deployed positions. The mechanism comprises a single piece of spring material (26) which is formed such that a first portion (10) engages with the projectile body (1) and a plurality of second portions (11) each exert a spring force on respective fins to deploy the fin and to latch it in its deployed position, the second portions (11) extending radially outward with respect to the first portion when deploying the fins.