The Type 23 frigates, also known as the Duke class due to them being named after famous dukes, were the last anti-submarine frigates designed for the Royal Navy before the end of the Cold War and most of which remain in service pending a replacement design. The Type 23s are based around the Type 2031Z towed array sonar as well as a Merlin ASW helicopter. Despite being designed primarily to hunt Soviet submarines in the North Atlantic, the Type 23 ships ended up being a very well rounded frigate design, with considerable anti-aircraft defenses (incorporating lessons learned from the Falklands War) thanks to their Sea Wolf VLS system as well as anti-ship capability from two quad Harpoon launchers. As a result of its towed array system, the Type 23 was designed to be among the quietest ships in the world, operating with a CODLAG system which would allow diesel propulsion during silent running and gas propulsion during normal operations. Some stealth characteristics are also incorporated. Since their introduction just before the end of the Cold War, the Type 23 ships have been modernized with numerous new weapons systems and sensors including a Type 997 Artisan radar, a more advanced Type 2087 towed array sonar, and CAMM missiles. This will keep the Type 23 fleet viable as the Royal Navy's principal anti-submarine force until the introduction of the Type 26 Global Combat Ship sometime in the next decade.

A total of 16 Type 23 ships were commissioned in the Royal Navy, the first in 1990 just before the Cold War ended. Three ships have been sold to Chile (the former HMS Norfolk, HMS Marlborough, and HMS Grafton) while the remaining 13 ships are still in British service. HMS Lancaster (F229) is known for being one of the few modern ships to skip NATO's ordinal pennant number system; its original number of F232 is identical to the Royal Navy's form for grounding a ship and was therefore considered unlucky.