On the east side of the shopping centre, adjacent to the canal.

The HMS Vernon Figurehead
Information Board
The HMS Vernon Figurehead
Information Board Text
The Noon Day Gun was originally fired to allow ships to check the accuracy of their marine chronometers, an instrument necessary for the accurate calculation of longitude. As light travels faster than sound observers would watch for smoke from the muzzle rather than listen for the sound of the cannon, a tactic which increased precision.
The practice of firing a gun at noon was widespread in European garrisons, particularly port garrisons. At One time, the signal was made from a man o' war, only later being taken over by the military garrison.
Portsmouth is not the only city to maintain the tradition of firing daily signals - Edinburgh Castle, Fort Henry in Kingston, Ontario, Signal Hill in South Africa and Vancouver all fire daily.
The Noon Day Gun is another of those little idiosyncracies that sets Gunwharf Quays apart and makes it such an exciting place to visit. This gun is a Royal Naval 12lb gun, forgeed in 1810 making it one of the oldest guns in the world still regularly fired. It would have originally been mounted aboard a warship and could fire up to 1,421 yards. It needed 8 men to operate, including a small boy 'the powder monkey' who would transfer gunpowder from the storage magazine in the hold to the gun crew.
The Noon Day Gun is fired at weekends and during special events and you can watch that ritual on the waterfront from 11.45am.