The only person from Northern Ireland to be awarded the Victoria Cross during World War II, was commemorated on Saturday.
James Magennis was recognised for his bravery in WWII
James Magennis, from west Belfast, won the medal while serving in the far east.
Mr Magennis took part in the midget submarine attack on the Japanese warship, Takao, in 1945.
Many people, some of them former submariners, turned out at Belfast City Hall to pay tribute to him.
Wreaths were laid at a stone and bronze memorial to the VC winner.
Mr Magennis's son, Paul, led the proceedings by laying the first wreath, while Lord Mayor Pat McCarthy also laid a wreath on behalf of the people of Belfast.
Mr Magennis was awarded the Victoria Cross in 1945 - but a memorial was not erected until 1999.
A display of memorial artefacts relating to J.J. Magennis was also on show inside the City Hall during the day, and members of the Submarine Association, and Mr Magennis's biographer, George Fleming, were on hand to answer questions.
On Friday, Belfast City Council and the Northern Ireland branch of the Submariners Association co-hosted a dinner to honour Mr Magennis's heroic actions.
The dinner was attended by former and serving submariners from all over the British Isles.
The Takao, badly crippled in an earlier torpedo attack, was guarding the entrance to Singapore harbour, and stood in the way of the Allied bid to reclaim the city.
During the daring mission to sink it, Mr Magennis had to leave the submarine to clean the hull of the ship so the limpet mines would attach and then manually release one of the mines which would not detach from their craft, the X23.
Wreths were laid at the memorial to Mr Magennis
The mines and high explosives detonated as planned and Takao settled upright on the bottom of the harbour.
This was the first time a naval diver had successfully exited and re-entered a min-sub not just once but three times.
Magennis was awarded the Victoria Cross for his role in the attack.
Lieutenant Ian Frazer, who commanded the vessel, also won the VC for his part and the other two members of the crew received lesser awards.
This was not the first dangerous attack in which Magennis had taken part, as he already had a Mention in Dispatches for his part in the attack on the German battleship Tirpitz earlier in the war.
When asked why he did the things that he had done, his modest reply was that he was only doing the job he had trained for.