The fort guns boomed out across the harbour and the Air Corps conducted a fly-past as part of commemorations on Spike Island to mark the 80th anniversary of the British handover of the 'Treaty Ports.'
The descendants of some of the Irish Army garrison who subsequently took control of the fortifications were among the guests at the commemoration.
The original Tricolour raised on the island in 1938 has been donated to its museum, along with the rope it flew from.
More than 100 members of the Defence Forces took part in the event.
The last post was played before the Tricolour was raised to a drum roll and the national anthem was played by the band of the 1st Brigade.
A 21-gun salute the boomed from the fort's 12-pounder coastal artillery guns and within seconds of it finishing four Air Corps PC9s conducted a low-level fly-past.
The fly-past by four aeroplanes in 'Eagle formation' was led by Captain Vincent Haigney and drew the impressive ceremonies to a close.
Cork County Council now own the island and have pumped significant money into turning it into an internationally-recognised tourist destination, which is expected to attract 50,000 visitors this year.
"Our goal is to get 100,000 visitors here per year in the next three years," council chief executive Tim Lucey told the gathering.
"When we get that figure the world is our oyster."