The policy adopted by the Royal Navy during the 1950s of acquiring separate types of frigates designed for specialised roles (i.e. anti-submarine, anti-aircraft and aircraft direction) had proved unsatisfactory. Although the designs themselves had proved successful, the lack of standardisation between the different classes led to increased costs during construction and also in maintenance once the ships became operational. Furthermore, it was not always possible to have the ships with the required capabilities available for a specific task. The first move towards creating a truly general-purpose frigate came with the Type 81 Tribal class which was initially ordered in 1956. The 24-knot speed of the Tribals was considered the maximum possible for tracking submarines with the new medium-range sonars, entering service. The type 81 gas turbine saw the frigates underway quickly, without taking hours flashing up steam turbines, and the provision of a helicopter for long-range attack were considered essential in the nuclear age. These ships were mainly intended to operate in the tropics but lacked the speed and armament required for the priority fleet carrier escort role East of Suez, where fast radar picket capability was important, as much as anti-submarine capability. So the new frigates would combine the roles of the T12 and T61. The fully air-conditioned Royal New Zealand Navy "Rothesay" class variant, , which gave all the crew a bunk and cafeteria messing and a RNZN commissioned design study for a more fully capable Type 12 frigate, which also assessed whether the Type 12 could carry 2 of the larger Wessex AS helicopters, was used as the basis of the RN Leander Improved Type 12 design.