Development:

 In the mid-1960s, the Royal Navy had a requirement for a replacement for the diesel-powered Leopard-class and Salisbury-class frigates. While the Royal Navy's warships were traditionally designed by the Ministry of Defence's Ship Department based at Bath, private shipyards (in particular Vosper Thorneycroft) campaigned for the right to design and build a ship to meet this requirement. Vospers claimed that, by ignoring what they claimed to be the conservative design practices followed by the MoD team at Bath, they could deliver the new frigate at a significantly lower price (£3.5 million compared with the £5 million price of the contemporary Leander class), while being attractive to export customers.

The class was ordered under political and Treasury pressure for a relatively cheap, yet modern, general purpose escort vessel which would be attractive to governments and officers of South America and Australasia -the traditional export markets of British shipyards. It was also envisaged as an out-of-area RN gunboat that would retain UK presence in those areas, as well as the Caribbean and the Gulf; essentially replacing the diesel Types Type 41, Type 61 and COSAG Type 81 with smaller crewed vessels. The RN staff disliked the idea and would have preferred, like many USN Admirals, to continue to develop steam types - in the RN's case, the Leander class, which was regarded as an especially successful and quiet anti-submarine hunter, but was seen by the politicians as dated and by the Treasury and export-oriented shipyards as too expensive to market. The development of Vosper's own export designs, the Mk 5 for Iran and the Mk 7 for Libya, increased the pressure on the Admiralty to accept this line of naval development, which seemed to offer a cheap export frigate with a range of 6,000 nm, a top speed of 37 knots, a superficially good armament of the new Mark 8 4.5 inch gun, facilities for a Westland Wasp helicopter, anti-ship missiles and two triple lightweight Seacat missile launchers. When plans for the new Libyan frigate, Dat Assawari, were finalised in 1968, the Admiralty board accepted its paper specifications were unanswerable and they would have to allow the shipyards to develop a low cost fill in a/s and general purpose version for the RN that would be stretched and fully gas turbine powered rather than CODAG like the Mk 5 and Mk 7. In reality, it was a much more difficult design, with the RN requiring the extra internal weight of the Computer Assisted Action Information System (CAAIS) computer command systems and the lack of heavy diesels or a steam plant low in the hull to balance the heavy top weight of CAAIS. The fitting of Tyne gas turbines for cruising, instead of the diesels used in the Iranian and Libyan versions, meant fuel consumption and cost would be high, which was a tremendous problem for the Royal Navy in the early 1980s when the austerity of early Thatcherism, cut the Royal Navy fuel allowance and meant most frigates spent more time tied up, rather than at sea in 1980-1, and despite the smaller crew, running costs of the Type 21 were ten percent higher than the Leanders. The Type 21 would provide the shipyards with experience in building fully gas turbine powered ships and provide them with useful work for the shipyards while the Type 42 destroyer and Type 22 frigate would not be ready until the mid-to-late 1970s. As the Admiralty design board were busy with the latter, the Type 21 project was given to private shipyards Vosper Thornycroft and Yarrow. The unmistakably yacht-like and rakish lines were indicative of their commercial design. Their handsome looks combined with their impressive handling and acceleration lent itself to the class nickname of Porsches.

At one stage, it was hoped to build a joint design that would meet both the Royal Navy's requirement for a low-cost Patrol Frigate and Australia's General Purpose Escort requirement, with discussions between the two navies beginning in 1967, with Australia, who hoped to build a series of the five Type 21s in Australian shipyards, part funding design work on the proposal. The requirements of the two navies were significantly different, with Australia wanting higher speeds (35 knots (65 km/h; 40 mph) rather than the 32 knots (59 km/h; 37 mph) requirement of the Royal Navy) and American armament (including Sea Sparrow missiles and a 5 inch Mark 45 gun), and Australia pulled out of the project in November 1968, later refining its requirements into the Australian light destroyer project.

A contract for detailed design of the new frigate to meet Royal Navy requirements and to build the first example was placed in March 1969. By this time cost had crept up to £7.3 million, more than Leander-class frigates.

Attempts continued to sell frigates derived from the Type 21 to export customers, including Argentina, while a broad-beam derivative armed with vertical-launch Sea Wolf surface-to-air missiles was offered to Pakistan in 1985.

The first of the eight built, Amazon, entered service in May 1974.

Design:

 These ships were the Royal Navy's first privately designed warships for many years. They were also the first design to enter service with the Royal Navy to be solely powered by gas-turbine engines, with two Rolls-Royce Tynes for cruising and two Rolls-Royce Olympus for high speeds arranged in a Combined gas or gas (COGOG) arrangement. The design made use of large amounts of alloy in the superstructure to lower the amount of topweight. Worries later surfaced about its resilience to fire, particularly following a major fire on Amazon in 1977 during which aluminium ladders distorted, preventing fire-fighting teams from reaching the blaze, and its ability to withstand blast damage. Later warships reverted to using steel.

As delivered, the Type 21s were armed with a single 4.5 inch Mark 8 naval gun forward, and a four-round launcher for the Sea Cat surface-to-air missile aft. The Italian Selenia Orion-10X lightweight fire control radar was adopted to control both the gun and the Sea Cat missile (as the GWS-24 system) in an effort to save weight. A Type 992Q air/surface radar was fitted, but a long-range air-search radar was not provided. A hangar and flight deck were provided for a single helicopter, at first the Westland Wasp. The CAAIS was provided to integrate the ship's weapons and sensor systems and provide the crew with all the relevant information they required to fight the ship, as and when they needed it.

In terms of automation, systems integration and habitability, they were well in advance of many of the ships that they replaced, such as the Type 81 frigate and Rothesay-class frigate - the latter's basic design could be traced back to 1945.

Modifications:

 When they entered service, the Type 21s were criticized for being under-armed in relation to their size and cost. A program was put in hand to increase their firepower by fitting four French-built MM38 Exocet anti-ship missiles. These were sited in front of the bridge screen aft of the forecastle, displacing the Corvus countermeasure launchers to amidships. This improvement was quickly carried out to all ships of the class except Antelope and Ambuscade; the latter was fitted with Exocet in 1984/5. The Exocets were located in two pairs and the missiles would deploy across the ship and clear the opposite side of the vessel to their launchers in flight. This differed from the later Type 22 frigates, where deployment of the missiles was to the same side of the vessel as the missile pairs were fitted. However, by the late 1970s it was clear the commercially designed Type 21 had 'insufficient margin' , of weight and space allowed in in house Royal Navy warship designs, for major modernization of the type being applied to the broad beam Leander frigates with the replacement of the subsonic Seacat missiles with anti missile Seawolf missiles to counter Soviet anti ship missiles and fitting of Type 2031 towed array sonar. Five modernization proposals for the Type 21s were considered by the Royal Navy and rejected by 1979 when it was 'reluctantly' decided not to modernize the class and it was estimated that they would be laid up by 1988.

The Westland Wasp, a single-role torpedo-carrying helicopter, was replaced by the vastly more capable multi-mission Westland Lynx when it became available. As and when ships came in for refit, ship-launched anti-submarine torpedoes were also fitted, in the form of two STWS-1 triple-tube launchers capable of firing United States USN/NATO-standard Mark 44 or Mark 46 torpedoes. After the Falklands War, two more 20mm Oerlikon guns were mounted, one each side of the hangar, to provide extra close-in armament on some ships of the class.

Analysis:

 Criticism was levelled at the performance of the type in the Falklands conflict. The ships developed cracks in their decks due to the different expansion properties of steel and aluminium. This was a vulnerability particularly demonstrated under the severe weather conditions that they encountered in the South Atlantic. Steel reinforcing plates were eventually fitted down the sides of the ships. Built to an exacting budget and design specification (and although carrying obsolete anti-aircraft weaponry), they distinguished themselves in a theatre for which they were not designed. As shore bombardment platforms and in lethal, accurate gunfire support for the Royal Marines and Army landing at San Carlos,they were superb, pinning down any possibility of Argentine army counterattack, but they remained shallow water surface fighting ships, designed for Vospers export market to provide nations like Libya and Iran with the firepower to replace the USA/UK as western supporting stabalisers under the Kissinger/ Healy strategy. In many ways the Iranian classification of their derivatives as small 'destroyers' is a more accurate classification than frigate. The Falklands revealed them useless for anti aircraft convoy defence with the Mk 8 4.5 gun having a large blind fire arc and the GWS24 Seacat over engineered for a simple missile. As anti submarine ships they were easily heard and classified by the ARA San Luis. Their speed and glamour amplified the ‘boy racer’ tendencies of the RN officer class which acted against quiet, anti submarine operation. They proved completely unsuitable for the Royal Navy's 1980s role as a second line nuclear deterrent, anti submarine force in the North Atlantic and Arctic and what sealed the fate of the class was their lack of margin to accept the 2031 towed array.

The class was also criticised for being overcrowded - at 384 ft (117 m), they had 177 crewmen compared to 436 ft (133 m) and just 185 crewmen for the modern Type 23 frigate. This was important at a time when the Royal Navy was facing a manpower shortage. The standard of accommodation for the officers was better than the RN average and the senior ratings enjoyed separate cabins - unlike the petty officers of the Type 42 destroyer of the same era, who slept in bunk rooms. The ratings' accommodation was also improved, with four-man sleeping berths leading off from the communal mess deck; again, far better than those of the Type 42 destroyer. In essence, the standard of accommodation and fitting were better, especially for officers, because it was a design intended to attract export orders. It is very little more than a stretched version of the MK 7 Vospers frigate built for third world Libya and, other than the fitting of CAAIS, with its electronic and intended weapon fit essentially the same as the Mk 7 prototype in type or level of sophistication. Higher automation and the new Mk 8 4.5 inch automatic gun combined with, in many ways, a much simpler electronic fit than the Leanders or Type 42, the new Type 21 class lacked both the long range radar, the Type 965, carried by most UK warships or the Limbo mortar and it associated sonar. Inevitably, that meant a much smaller crew than the Leanders, with little capability to modernise (owing to its small size) and already being close to its topweight limit; the Type 21's days were numbered. A decision not to modernize them was made in 1979 even before the Falklands losses. The several hundred tons of ballast that had to carried low down meant that the frigates could not usually achieve their planned 35 knots speed for any long distance, but the ships were all still good for a dramatic 37 knot burst speed, with two ships claiming to have exceeded 40 knots on more than one occasion. Nevertheless, these ships were regarded favorably by their crews and proved to be highly maneuverable and reliable assets in a navy suffering depletion in the number of modern escort hulls.

Service:

 Excepting Amazon, all the class took part in the 1982 Falklands War as the 4th Frigate Squadron. They were heavily involved, performing extensive shore-bombardment missions and providing anti-submarine and anti-aircraft duties for the task force. On 10 May, HMS Alacrity and Arrow probed through Falkland Sound at night searching for minefields that might have impeded landings and operations, almost as expendable hulls. Alacrity engaged and sank an Argentine naval supply vessel in the Sound. On exiting the Sound at daybreak, they were attacked by the ARN submarine San Luis, which fired two torpedoes; one hit Arrow's submarine towed decoy (as intended) and the other bounced off her hull, having failed to arm itself. Two ships were lost: Ardent was hit by bombs dropped by Argentine aircraft on 21 May and was consumed by fire; Antelope was hit by bombs on 23 May, one of which was set off by the bomb disposal team attempting to defuse it on 24 May, causing the ship to catch fire, setting off her magazines resulting in her breaking her back and sinking.

Sale to Pakistan:

 The six surviving Type 21 frigates were sold to Pakistan in 1993-1994. The class was renamed by the Pakistani Navy as the Tariq class, after the first vessel that was acquired, the PNS Tariq, formerly Ambuscade. All six ships remain in service, as of 2011. They have had their Sea Cat launcher removed, as well as their Exocet missiles. Three of the ships had their Exocet missiles replaced by the more capable US-made Harpoon missile, the other three were fitted with the Chinese 6-cell LY-60N Hunting Eagle surface-to-air missile system.

source: wikipedia