The crew of Rescue 116 has been remembered in an emotional wreath-laying ceremony during which four flares were set off - one for each lost hero.
More than 800 people attended the event for the victims of the tragedy, including Captain Dara Fitzpatrick's sister, Niamh.
The commemoration, organised by the RNLI lifeboat service off Dunmore East, Co Waterford, also included rescue workers from across the country.
Niamh Fitzpatrick was on board the RNLI boat from which one wreath was dropped into the waves.
Dunmore, Tramore, Fethard and Kilmore Quay lifeboats, along with Dunmore East Coast Guard, set sail ad also laid wreaths.
The Rescue 117 helicopter, based in Waterford, where Capt Fitzpatrick was previously stationed, performed two fly-overs as the ceremony took place.
Four flares were set off and a minute's silence was observed for each of the crew members.
A book of condolence has been opened at the lifeboat station in Dunmore East.
RNLI spokeswoman Niamh Stephenson said organisers were touched by the support from rescue workers and locals.
"It started with the Dunmore East RNLI as a very local event, they wanted to do something locally just to lay a wreath at sea and it snowballed from there," she said.
Ms Stephenson added that it was a "very, very emotional day" and that the RNLI was overwhelmed by the "incred- ible" turnout.
The bodies of Capt Fitzpatrick and co-pilot Capt Mark Duffy have been recovered since the Irish Coast Guard helicopter crashed in the early hours of March 14.
Winch operator Ciaran Smith and winchman Paul Ormsby have still not been located.
Preliminary investigations by the Air Accident Investigation Unit (AAIU) found that a database for obstacles used by the Rescue 116 helicopter did not feature Blackrock island.
It also noted that the locator beacons on the crew's lifejackets did not emit any signals after the crash.
CHC, the company that supplies the Sikorsky S-92A helicopter involved in the tragedy, said it was carrying out an internal review into its systems.
It also expressed its sympathies to the families of the four crew members.