Leander-class frigate

The Leander-class, or Type 12I frigates, comprising twenty-six vessels, was among the most numerous and long-lived classes of frigate in the Royal Navy's modern history. The class was built in three batches between 1959 and 1973. It had an unusually high public profile, due to the popular and acclaimed Warship BBC television drama series.

The Leander design or derivatives of it were built for other navies:
 * Royal New Zealand Navy as the Leander class
 * Chilean Navy: Condell class
 * Royal Australian Navy: River class
 * Indian Navy: Nilgiri class
 * Royal Netherlands Navy: Van Speijk class

Design
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. This improved Type 12 will be known as the Leander class. The hull and steam turbine machinery will be substantially the same as for the Whitbys. 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. We shall also introduce air conditioning and better living conditions." The 1963 edition of Jane's Fighting Ships described it as a "mainly anti-submarine but flexible and all purpose type".

"The Leander class have the same hull and substantially the same steam turbine machinery as the Whitby class, but are a revised and advanced design and will fulfil a composite anti-submarine, anti-aircraft and air direction role. The 40mm guns will eventually be replaced by Seacat ship-to-air launchers. The ships are equipped with VDS (Variable Depth Sonar), formerly known as dipping asdic."

The Y160 boiler variant used on the Batch 3 Leanders (such as Jupiter) also incorporated steam atomisation equipment on the fuel supply so the diesel fuel entering the boilers via the three main burners was atomised into a fine spray for better flame efficiency. Some Y100 Boilers were also converted to steam atomisation, HMS Cleopatra being one of them. The superheat temperature of the Y160 was controlled manually by the boiler room petty officer of the watch between 750 - 850 °F and the steam supplied to the main turbines was at a pressure of 550 psi. The Leander-class frigates did have Babcock and Wilcox boilers but of a more conventional two-drum design, one water drum and one steam drum, much like a Yarrow boiler without the second water drum. The water drum was offset to one side and below the furnace and steam drum. The two boilers fitted were 'handed' with the water drum inboard on both. Many Leanders had six burner furnaces (known as Five and a Half Boilers) and the output was varied by altering the number of burners in use.

Construction programme

 * Royal Navy

Midlife major refits
The entire class was given a standard weapons fit when built, with a 4.5in gun mount, Seacat missile system and Limbo ASW mortar. However, advances in weapons systems led to a number of different conversions being undertaken on various members of the class. This saw the class grouped into four broad batches:
 * Ikara - installation of the Ikara ASW missile system in place of the 4.5in gun mount.
 * Exocet/Seacat - installation of Exocet anti-ship missile system in place of 4.5in gun mount, plus additional Seacat surface-to-air missile systems.
 * Exocet/Seawolf - installation of Exocet anti-ship missile system in place of 4.5in gun mount; replacement of Seacat with single Seawolf surface-to-air missile system.
 * Gun - retained 4.5in gun mount and Seacat missile system.

Batch 1, Ikara conversion
Eight of the first ten Leanders were given the so-called "Batch 1" or "Ikara" conversion, which saw the Ikara anti-submarine warfare missile installed in place of the 4.5in gun, plus an additional Seacat system.

Batch 2, Exocet conversion
Two of the Leanders with Y-100 machinery, and five out of the six with Y-136 machinery, were given the so-called "Batch 2" or "Exocet" conversion. This conversion gave them Exocet anti-shipping missiles in place of the 4.5in gun mount, 2 additional Seacat systems, and the ability to operate the Lynx helicopter.

Batch 2, navigational training ship conversion
Juno, commissioned 18 July 1967 was converted to serve as a navigational training ship. Work at Rosyth began in January 1982 and completed in February 1985.

Batch 3, Seawolf conversion


The Seawolf conversion gave the broad-beamed Leanders Exocet anti-shipping missiles in place of the 4.5in mounting, a Seawolf missile system in place of Seacat, Sonar 2016, and the ability to operate the Lynx helicopter. 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.

† = Latest estimate as at 14 December 1983.

Batch 2 TA & Batch 1B - towed array conversions
In 1981 the Admiralty said that intended to devote "substantial resources to improving the effectiveness of the sensors and anti-submarine weapons ... This includes the new passive towed array system that we hope to introduce into service next year."

The former destroyer Matapan and the frigate Lowestoft were used for testing prototypes in 1978-81. It was planned to install them on Rothesay conversions, but this was not possible due to industrial strikes. Scheduling then made it easier to fit them on board four of the Batch II Leanders. "Compensation for the additional 70 tons of top weight included lowering the Exocet launchers. This interesting quartet was to have been followed by five Batch III Leanders, but the latter fell foul of the Nott cancellations.  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."

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 only sensible, cost-effective option open to us was to take some relatively older ships - the Leanders - and convert them quickly to the towed array. We have done that with great success, and the peacetime patrols have achieved some remarkable results, but there has been a price to pay because of the age of those ships."

In general, "as a ship gets older it tends to get noisier - the hull and also the propulsion system". Admiral Sir Julian Oswald spoke "to counter the presumption that older ships get noisier. That is not necessarily true and it is not true, in my experience, in the case of the Leanders because understanding of ship generated noise is improving all the time and our techniques for countering it are improving - our noise monitoring and so on - so, despite the fact that these ships are getting older, they are in many cases managing to improve their performance with regard to ship noise." Captain Geoffrey Biggs said "the Leanders are remarkably quiet in operation and our experience has been that they have made excellent towed-array platforms despite the rather short notice of actually getting the towed-array programme together to start with. They actually perform very well."

Five ships were converted to use Waverley Type 2031(I) towed array (passive search very low frequency). They were as follows:

Royal Navy service
The ships performed excellently in Royal Navy service, with relatively low noise levels giving the 2031(I) towed sonar mounted during the 1970s a range of more than 100 miles, better than that of the more advanced 2031(Z) sonar when fitted in the Type 22 class. However, all Leanders in Royal Navy service were decommissioned by the early 1990s due to the ships' aging design and the high number of crew. Scylla was sunk 27 March 2004 as an artificial reef off Cornwall, ten years after her decommissioning in 1994.

Overseas service
Leander-class frigates were also successfully exported to serve in the Royal New Zealand Navy and Chilean Navy; in the latter they were designated as the Condell class. Further Leander-class frigates were built under licence in Australia as the River class for the Royal Australian Navy, India as the Nilgiri class and the Netherlands as the Van Speijk class. Royal Navy ships were sold to the navies of Chile, Ecuador, New Zealand (Bacchante becoming HMNZS Wellington and Dido becoming HMNZS Southland), India and Pakistan.

No original Leanders remain in service, but the Indonesia ex-Van Speijk class are still in service. Pakistan decommissioned the last of its Leander-class frigates, Zulfiqar, in January 2007, Ecuador decommissioned both her Leanders in 2008. India decommissioned her last Leander on 24 May 2012.

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.

Fate

 * Royal Navy