Type 21 frigate

The Type 21 frigate, or Amazon-class frigate, was a British Royal Navy general-purpose escort that was designed in the late 1960s, built in the 1970s and served throughout the 1980s into the 1990s.

In the mid-1960s, the Royal Navy (RN) had a requirement for a replacement for the diesel-powered Leopard-class (Type 41) anti-aircraft frigates and Salisbury-class (Type 61) air direction 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 Persian Gulf; essentially replacing the diesel-powered Type 41s and Type 61s and the combined steam and gas-powered Type 81 frigates with smaller crewed vessels. The RN staff disliked the idea and would have preferred to continue to develop steam types – in the RN's case, the Type 12I Leander class, which was regarded as a 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.^{[citation needed]}

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 nautical miles (11,000 km; 6,900 mi), a top speed of 37 knots (69 km/h; 43 mph), a superficially good armament of the new Mark 8 4.5-inch (113 mm) 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 that its paper specifications were unanswerable and they would have to allow the shipyards to develop a low cost fill in anti-submarine warfare and general purpose version for the RN that would be stretched and fully gas turbine-powered rather than combined diesel and gas like the Mk 5 and Mk 7. In reality, it was a much more difficult design, with the lack of heavy propulsion machinery low in the hull to balance the top weight of bulky superstructure. 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 that most frigates spent more time tied up, rather than at sea in 1980–1981; and despite the smaller crew, running costs of the Type 21 were ten percent higher than those of the Leanders.^{[citation needed]}

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 the private shipyards of Vosper Thornycroft and Yarrow. The unmistakably yacht-like and rakish lines were indicative of their commercial design.^{[citation needed]}

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 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-knot (59 km/h; 37 mph) requirement of the Royal Navy) and American armament (including Sea Sparrow missiles and a 5-inch (127 mm) Mark 45 gun). Australia pulled out of the project in November 1968, later refining its requirements into the Australian light destroyer project. After the Royal Australian Navy (RAN) DDL was cancelled the RAN and Royal New Zealand Navy (RNZN) reconsidered the Type 21 but still found it too expensive, and considered the UK gun and radar inferior to the United States Navy options. Australia ordered the US Oliver Hazard Perry-class design in 1976.

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. A broad-beam derivative armed with vertical-launch Sea Wolf surface-to-air missiles was offered to Pakistan in 1985.