Claim: Green Mace was a 102 mm British heavy anti-aircraft gun developed by Vickers in the 1950s.
Evidence: A proof of concept prototype was built with a 4.02 inch (102 mm) barrel, but otherwise was as intended. Green Mace, also known as the QF 127/58 SBT X1, was a British heavy anti-aircraft gun of the 1950s. The gun was developed by Vickers under the direction of the Royal Armaments Research and Development Establishment at Fort Halstead. 
102mm Heavy anti-aircraft gun United Kingdom Vickers 1956