The British frigate programme of 1951 resulted in four types of specialized frigates:

• - Anti submarine (Type 12),

• - Anti-aircraft (Type 41),

• - Aircraft direction (Type 61) and

• - Utility (Type 16).

However there was a clear requirement for a class of general purpose frigates. A standardized design would not only be cheaper to construct and operate but the multi-role capability would make operational deployments easier. This requirement was partly fulfilled by the Tribal class, although these vessels had insufficient armament and speed to act in an escort role and were consequently employed mainly in the Far East and at foreign stations. Plans to build further Tribal class frigates were abandoned in favour of modifying the Type 12 design.

Design work on updating the Type 12 design began in 1958. Whilst the hull and machinery of the Whitby class and Rothesay class Type 12 frigates remained largely unchanged, the superstructure was redesigned as a single block and incorporated a helicopter hangar. Fully air conditioned the modified vessels would have better living and working conditions than their predecessors and would be more resistant to nuclear and chemical warfare. For example, they were built without portholes. With a standard displacement of 2,450 tons they would measure 372 ft in length, 41ft in beam and 18ft in draught. Powered by two Babcock and Wilcox boilers they were designed for a speed of 30 kts and a complement of 251. The armament was tailored to suit their general purpose role. They would carry 4.5 inch Mk6 twin mounting while for close range air defence they were designed to carry a Seacat launcher on the hangar roof. Anti submarine defence would consist of a single Mk10 three barrelled anti submarine mortar (Limbo) mounted aft of the flight deck, and the Westland Wasp helicopter.

These features from the County class destroyers were also incorporated including a bridge that provided better visibility and hydraulic power systems to drive the Seacat lifts and various winches. This feature also reduced the manpower needed on deck to operate the Leander Class. The Leander class was noted for its strong performance in poor weather and heavy seas. This was made possible through twin rudders, twin propellers and non-retractable fin stabilisers.