Missile development, rising cost and obsolescence

Gun systems change comparatively slowly even while metallurgy, shells and explosives improve. Missile technology develops faster and demands repeated work against improving threats. Better performance raises costs, restricting the number a navy can afford. An opponent's response creates pressure for another improvement and further expense. The tradeoff between speed, price and quality becomes especially difficult when a slow programme can deliver an outdated weapon. Work on a successor therefore needs to begin while the existing missile is still in service.