There have been a number of 21-inch torpedoes in service with the Royal Navy of the United Kingdom.
A Mark IV torpedo being hoisted onto HMS Monarch, an Orion-class battleship, during the First World War.
Launch of a Mark VII torpedo from HMAS Australia, during trials in 1927.
A Mark 20 torpedo exhibit at the Clandestine Immigration and Naval Museum, Haifa, Israel.
A Mark 23 torpedo repainted as an advertisement in front of The Ancient Mariner restaurant in Lynmouth, United Kingdom.
The Mark 24 Tigerfish was a heavyweight acoustic homing torpedo used by the Royal Navy during the 1980s and 90s. Conceptual development dates to the mid-1950s, and formally started in 1959 with a targ
British 21-inch torpedo
…the speed to counter upcoming nuclear submarine designs. The seeker head development was transferred to Project Ongar, which would later become the Mark 24 Tigerfish. A wire-guided version of the Mark 20 separately developed by Vickers Shipbuilding and Engineering (VSEL) as a private venture. Development commenced…