A missile is housed in a launcher from which it is launched by efflux gases from a thrust motor of the missile. A closure device is secured by retaining screws in a position in which it closes off the rear end of the missile and embodies a thrust generating cartridge which is fired to propel the device clear of the rear end of the missile. The closure device comprises a demand cap and base plate and the cartridge generates thrust first to release the cap and plate from the screws and then to displace the domed cap relative to the base plate to bring them to a disposition in which the momentum of the domed cap is imparted to the complete closure device thereby to propel the cap and the plate together at velocity determined by the motion of the domed cap relative to the base plate.
