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.

[6] On 7 March 1960, the Civil Lord of the Admiralty C. Ian Orr-Ewing stated that the "Type 12 Whitby-class anti-submarine frigates are proving particularly successful ... and we have decided to exploit their good qualities in an improved and more versatile ship.

The main new features planned are a long-range air warning radar, the Seacat anti-aircraft guided missile, improved anti-submarine detection equipment and a light-weight helicopter armed with homing torpedoes.

A hangar and flight deck were provided aft for the Westland Wasp light anti-submarine helicopter, which was still at the prototype stage when the first ships were ordered.

The ships were all given names which had previously been given to Royal Navy cruisers, mostly of characters from classical mythology, the exceptions being Cleopatra and Sirius.

The superheat temperature of the Y160 was controlled manually by the boiler room petty officer of the watch between 750–850 °F (399–454 °C) and the steam supplied to the main turbines was at a pressure of 550 psi (3,800 kPa).

[29] This conversion gave them Exocet anti-shipping missiles in place of the 4.5-inch gun mount, 2 additional Seacat systems, and the ability to operate the Lynx helicopter.

[32] Only five of the broad-beamed Leanders were converted to carry Seawolf due to costs (£70 million for each refit) and, as a lesser consideration, to retain some ships capable of naval gunfire support.

A fifth Leander, the Ikara-carrying HMS Arethusa, was fitted with a towed array in 1985, the year the towed-array trials ship Lowestoft was withdrawn from service.

"[38] Admiral Sir Julian Oswald said to the Defence Committee in 1989, "in order to capitalise on the really very exciting and important development of towed arrays, we had to get them to sea as soon as we could.

The 1973 and 1975–1976 Cod Wars in the latter of which HMS Diomede suffered severe damage with a 30 feet gash in its hull after being rammed by an Icelandic Coast Guard gunboat.

[45] The five unconverted, gun-armed, broad-beam Leanders, arrived in the war zone in the last week of the conflict and immediately after it to serve with the post-war task force led by the brand new carrier HMS Illustrious.

An Argentine naval dive team planned to place limpet mines on HMS Ariadne at Gibraltar during the conflict (Operation Algeciras).

However, all Leanders in Royal Navy service were decommissioned by the early 1990s due to the ships' ageing design and the high number of crew.

Starting in 1986, the six Van Speijk-class ships were sold to the Indonesian Navy and renamed the Ahmad Yani class, five of which are still in service.

[53] HMNZS Canterbury, the last steam-turbine driven Leander-class frigate in the Royal New Zealand Navy, was decommissioned in Auckland on 31 March 2005 after 33 years operational service.

In 2006 it was announced that the ship was to be sunk as a dive attraction in the Bay of Islands, and this was carried out on 3 November 2007 at Deep Water Cove.