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.

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. 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). 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 outboard on both. Many Leanders had seven burner furnaces and the output was varied by altering the number of burners in use.

General characteristics
Type:	Frigate
Displacement:	2,500 tons (later 2,790 tons) standard 2,962 tons (later 3,300 tons) full load
Length:	113.4 metres (372 ft)
Beam:	13.1 metres (43 ft)
Draught:	4.5 metres (15 ft)
Propulsion:	2 Babcock & Wilcox oil-fired boilers, geared steam turbines, 22,370 kilowatts (30,000 hp), 2 shafts
Speed:	27 knots (50 km/h; 31 mph)
Range:	7,400 kilometres (4,600 mi; 4,000 nmi) at 15 knots (28 km/h; 17 mph)
Complement:	260
Sensors and processing systems:	Radar Type 965 (air warning radar removed in batch 1 ships), Type 992 Q, Type 903, Type 974/978 Sonar Type 162,184,199, later type 2031 towed array sonar
Armament:	Initial 2 4.5 inch guns (1 twin mounting Mk6) 1 Seacat surface to air missile launcher 2 20mm guns (single mountings) 1 ASW Limbo mortar Batch 1 1 Ikara Anti submarine missile Launcher 2 Seacat surface to air missile Launchers 2 40mm guns - single mountings Two triple 324 mm (12.75) STWS-1 tubes for Mk 46 and Stingray ASW torpedoes 1 Limbo ASW Mortar Batch 2 four MM.38 Exocet anti ship missile launchers 3 Seacat surface to air missile Launchers 2 40mm guns - single mountings Two triple 324 mm (12.75) STWS-1 tubes for Mk 46 and Stingray ASW torpedoes Batch 3 four MM.38 Exocet anti ship missile launchers. One sextuple GWS.25 launcher with 30 sea wolf SAMS. Two 20mm AA guns. Two triple 324 mm (12.75) STWS-1 tubes for Mk 46 and Stingray ASW torpedoes
Aircraft carried:	Initial and Batch 1 One Westland Wasp ASW helicopter Batch 2 and Batch 3 One Westland Lynx HAS.Mk 2 ASW helicopter