An ammunition unit, such as a missile, the casing of which contains at least one explosive charge as well as warhead modules arranged in or on the fuselage or casing that comprise a constituent part of the unit's warhead function when the explosive charge is actuated. The warhead effect modules are of modular design, and the various modules are secured to the fuselage or casing by securing devices and/or retention parts. The device includes a range of modules pertaining to different types of warhead effects. When engaging an actual type of target the ammunition unit is assembled with an array of modules-selected from the range of modules-matched to different types of targets or engagement situations, with the array of modules secured to the fuselage or casing by securing devices.