A £23,300 hand-out will revamp an education centre at Coalhouse Fort, Tilbury.
The centre will show how the original guns would have been manned and operated when the fort was built in 1874.
Tilbury power station operator, RWE Npower, donated the money which will be spent on building restoration, re-roofing, educational materials and a life-size replica of the gun.
The cash will also help restore the Victorian coastal defence fort to its original condition.
Project worker Ian Donaldson said: "We are really grateful for this money, which is the first major restoration grant received by the fort since it was handed over by the military in 1962.
"We intend to complete this project as soon as possible so we can open this new and exciting attraction to the public."
Peter Smith, engineering manager at Tilbury Power Station, said: "I am really pleased to present the Coalhouse Fort Project with this money, as it is an extremely worthy cause and highlights RWE Npower's commitment to being a responsible and supportive neighbour."
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