The organisation has made only 81 such awards, mostly to British recipients, and the Armstrong disappearing gun at Taiaroa Head is one of only six recipients outside Britain, and the only one in this country.
The Dunedin six-inch gun was installed about 1889, after fears of a Russian naval attack, and was part of Dunedin's ''Fort Taiaroa'' defences.
The weapon was designed to ''disappear'' by automatically dropping into the relative safety of a gun emplacement for reloading.
It is the only fully-restored Armstrong disappearing gun still in its original firing position in New Zealand, and is also a rarity in world terms.
The Institution of Mechanical Engineers UK recently told Laurie Stewart, convener of the Fort Taiaroa education and resource group, the award application was successful.
And he paid tribute to members of the New Zealand Antique and Historical Arms Association's Otago branch, for their extensive restoration work.
A plaque is being made to mark the award, and this will be presented by an institution representative at a ceremony in Dunedin later this year.
Association former branch chairman Stuart Maxwell said that restoring the gun had been ''a big part of my life'' and the award was a ''marvellous'' outcome.
Dunedin resident Jean Park was ''really thrilled'' about the award, which further highlighted Dunedin's wealth of heritage tourism attractions. Mrs Park (70) said the award was ''hugely significant'' and she had been ''determined that it was going to happen''.
It would give Dunedin people another reason to celebrate their many heritage treasures, and attract more tourists.
The award had arisen from a trip by Alan Park, a British mechanical engineer and member of the institution, who lives in northern England, to his cousin, Ian (Mrs Park's husband), in Dunedin in early 2011.
They had visited the gun at Taiaroa Head, and Alan Park, who was amazed by the condition of the gun, had raised the possibility of the award.
Mrs Park had then contacted the Otago Peninsula Trust, parent body of the Fort Taiaroa group, suggesting it make an application for the award, and then had kept in touch with Alan Park.
The disappearing gun was one of a series of hydraulically-operated inventions developed by Lord Armstrong, a 19th-century British inventor.
