These ships were the Royal Navy's first privately designed modern frigates. They were also the first design to enter service which used solely gas-turbine propulsion, as opposed to the steam turbines or diesel engines of their predecessors. The design made use of large amounts of aluminium alloy in the superstructure to lower the amount of topweight but 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. Later warships reverted to using steel again.
As originally built, the Type 21 design made use of a lot of "off the shelf" technology, such as the old Sea Cat missile (combined with the Italian-built Alenia Orion-10X fire-control system - as the GWS-24 system), the Wasp anti-submarine helicopter, and marinized Rolls-Royce aircraft engines. Yet it also featured modern electronics such as the CAAIS (Computer Assisted Action Information System) system 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 their older Royal Navy contemporaries, such as the Type 81 frigate and Rothesay-class frigate, the latter of whose basic design could be traced back to 1945.
| General characteristics | |
|---|---|
| Type: | Frigate |
| Displacement: | As built;
|
| Length: | 360 ft (109.7 m (w/l)) 384 ft (117 m (o/a)) |
| Beam: | 41.8 ft (12.7 m) |
| Draught: | 19 ft (6.8 m) |
| Propulsion: | COGOG on 2 shafts;
|
| Speed: | 32 kt (Olympus) / 18 kt (Tyne) |
| Range: | 4,000 nmi at 17 kt |
| Complement: | 13 officers, 164 ratings |
| Sensors and processing systems: | 1 x Radar Type 992Q low-level search |
| Armament: |
|
| Aircraft carried: | 1 x Wasp or Lynx |
| Aviation facilities: | Flight deck and hangar |
When they entered service, the Type 21s were immediately criticized for being woefully under-armed. A program was put in hand to increase their firepower by fitting 4 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, with the latter 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.
The Westland Wasp, a single-role torpedo-carrying helicopter, was replaced by the vastly more capable multi-mission Westland Lynx when it became available. Ship-launched anti-submarine torpedoes were also fitted as and when ships came in for refit, 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 each side of the hangar to provide extra close-in armament on some ships of the class.
