Type 21-class

The Type 21, or Amazon-class frigate, was a general-purpose escort designed in the late 1960s to replace the Type 41 and Type 61 classes. In a departure from traditional Ministry of Defence design practices, the project was awarded to the private shipyards Vosper Thornycroft and Yarrow. The class was intended to provide a modern, lower-cost vessel that would be competitive in export markets. Australia initially participated in the development process but withdrew in 1968 due to differing requirements regarding speed and armament.

The design utilized an all-gas-turbine propulsion system in a combined gas or gas (COGOG) arrangement. To reduce topweight, the ships were constructed with a large aluminum alloy superstructure. This design choice later prompted concerns regarding fire resistance and structural integrity under blast conditions. The ships featured high levels of automation and a Computer Assisted Action Information System (CAAIS) to integrate sensors and weaponry. Internal layouts provided improved habitability compared to preceding classes, including separate cabins for senior ratings. During their service lives, the vessels developed structural cracking in the hulls when operating in severe weather, which required the installation of steel reinforcing plates for stabilization.

Eight vessels were completed between 1974 and 1978. In 1982, seven ships of the class were deployed as the 4th Frigate Squadron during the Falklands War. These vessels conducted shore bombardment, anti-submarine patrols, and air defense duties. During the conflict, HMS Alacrity engaged and sank an Argentine supply ship. The class sustained the loss of two vessels, HMS Ardent and HMS Antelope, following Argentine air attacks.

The six surviving ships remained in Royal Navy service until 1993–1994, when they were sold to the Pakistan Navy and renamed the Tariq class. In Pakistani service, the ships underwent modifications to their sensor suites and armament, including the installation of different surface-to-air and anti-ship missile systems. By the 2020s, the majority of the class had been decommissioned, with several units expended as targets during naval exercises.