OVERVIEW:  The Mk 23 “Grog” is a heavyweight Royal Navy submarine-launched torpedo developed for anti-submarine warfare. It features wire guidance with passive acoustic homing and dual-speed operation.

DETAILS:  “Mk 23” designates its place in the Royal Navy’s 21‑inch torpedo series and “Grog” was the project codename. It is based on the Mk 20 design, measuring approximately 4.54 m in length, 533 mm diameter, weighing around 907 kg, and carrying an 89 kg Torpex warhead. It uses an outboard wire-dispenser for mid-course guidance and switches to passive sonar homing in the terminal phase. It offers dual-speed modes (~18–20 kn search and ~28 kn attack). Initial prototypes were tested in the mid-1950s, production torpedoes were delivered in 1959, entered service in 1966, achieved full operational capability by 1971, and remained in RN service until being replaced by the Mk 24 Tigerfish in 1987.

TYPE: Heavyweight submarine-launched wire-guided acoustic homing torpedo

FUNCTION:  Launched from 533 mm submarine tubes, it uses wire guidance during mid-course to navigate past decoys, then transitions to passive sonar homing for final approach. It accelerates from a lower-speed searching mode to higher-speed attack mode before detonating its warhead on contact.

NOTE:
IOC: entered service 1966; fully operational 1971; retired 1987
Manufacturer: Royal Navy Underwater Weapons Establishment (UK)
Operators: United Kingdom
Platforms: Royal Navy Triton Super-T conversions, Porpoise-class, Oberon-class, Swiftsure-class submarines (interim loadout prior to Tigerfish)
Conflict used in: no confirmed combat deployment

SOURCE: British 21‑inch torpedo (Wikipedia); NavWeaps “Post‑World War II Torpedoes of the United Kingdom”; Cold War RN torpedo armament (Naval‑Encyclopedia); Mk 23 Grog technical history (British 21‑inch torpedo page)