The Type 21 frigates were intended as a class of general purpose frigates to replace the diesel-powered frigates of the and es, and to maintain the Royal Navy's frigate numbers until the specialist anti-submarine ships of the Type 22 class could enter service. The contract for the design of the class was placed with the commercial shipbuilder Vosper Thornycroft, with the intent that the design would be cheaper than those produced by the Royal Navy's own design staff, while being attractive for export buyers.