The bravery of a Chepstow sailor awarded the Victoria Cross at Gallipoli in Turkey in 1915 was being marked at a service in the town.
Williams was recalled to action in the war (Picture Chepstow Museum)
William Williams died in the arms of his commanding officer who said he was the "bravest sailor he had ever met".
He jumped into the sea braving gun fire to help other troops ashore before he was killed.
Members of the seaman's family were expected at the Chepstow Anzac Day service.
Able Seaman Williams, who was 34 and single, died exactly 91 years ago, on 25 April, 1915.
He later became one of only 39 people to receive the VC in the Gallipoli campaign, which saw 100,000 allied lives lost.
He stood alongside the commander of the HMS River Clyde, Captain Edward Unwin, and two other sailors, chest deep in the sea holding a rope keeping the drifting lighters together and helping two battalions to disembark at Gallipoli's V beach.
A picture of the events hangs in the church (Picture Chepstow Museum)
The official entry in the Register of VCs says: "He was eventually dangerously wounded and later killed by a shell whilst his rescue was being effected by his commander who described him as the bravest sailor he had ever met".
Henry Benjamin, treasurer of Chepstow Royal Naval Association, which is organising Tuesday's memorial said they had been holding the service for the last five years.
"It's one of about 10 held around the UK, but unique in Wales," said Mr Benjamin, adding they believed the bravery of the seaman, who was a reservist called up for action had to be recorded.
He said members of the sailor's family, some who live in nearby Caldicot, attend the memorial each year.
Williams' commander stood with him in the sea (Picture Chepstow Museum)
Chepstow museum has a large display dedicated to AS Williams - the town's only Victoria Cross winner in World War I.
Museum curator Ann Rainsbury said the sailor, who was born in Shropshire, had been recommended for his bravery before Gallipoli, including while serving in South Africa and China.
"He had joined as a boy sailor and come out of the Navy in 1910, " she said.
"His service expired in September 1910 and he transferred to the Royal Fleet Reserve but he was recalled to active service in August 1914, and died on 25 April, 1915 at V beach in Gallipoli".
Before he was recalled, Williams was in the police force in Newport, St Mellons and Risca, and also worked at the Orb steel works in Newport.
There are two memorials to the sailor in Chepstow - a painting showing his bravery at Gallipoli in St Mary's Church as well as a gun from a German submarine presented by King George V.
The actual VC which King George presented to Williams' father in 1916 is now in private ownership.