Why missile defence belongs to different services

Why do some countries place missile-defence forces in the army, air force, navy, or a separate branch?

Organizational ancestry matters: missile units may grow from artillery, strategic rockets, aviation, or naval air defence. Britain relies mainly on service-level systems rather than a costly national shield.

Missile-defence organizations often inherit the service that developed their underlying weapons. Systems derived from artillery or strategic rockets tend to remain with armies, while other countries place them with air forces or navies. In Britain, Type 45 is the principal maritime contribution and Sea Ceptor provides the basis for army and Royal Marines air defence. Navalized equipment suits the Marines because it is already designed for salt water and movement by ship. A national ballistic-missile shield is a different proposition because of its high cost and uncertain gain. Britain's own ballistic missiles support a deterrence strategy that competes with spending on interception.