World War II veteran John "Harry" Kellers beamed from his folding chair Sunday morning, underneath a shade tent in the sweltering East Patchogue heat, as dozens of friends, family and well-wishers sang "happy birthday" in honor of his century of life.

Kellers was just 18 years old and fresh out of Patchogue High School, where he was a star pitcher for the baseball team, when he landed on Omaha Beach as part of the D-Day invasion of France on June 6, 1944.

Manning an artillery cannon on a Navy landing craft, he fought for hours alongside about 34,000 other American service members on that stretch of beach -- more than 2,300 of whom were killed by Nazi forces, according to the National World War II Museum. Kellers completed military service in the Pacific before becoming a power plant technician and raising a family in East Patchogue, where he still lives a stone’s throw from the Great South Bay, his family said

In recognition of Kellers’ service and his 100th birthday, he received official proclamations and honors from Suffolk County Executive Edward P. Romaine, State Sen. Dean Murray (R-Brookhaven), Brookhaven Deputy Town Supervisor Neil Foley and others Sunday. The ceremony followed a parade with Hagerman Fire Department trucks, Suffolk County Police Department cruisers, a helicopter and decommissioned military Jeeps.

"There's less than 50,000 World War II veterans alive today, 80 years since the end of the war," said Roger Kilfoil of Mission Margraten Plus, a Brooklyn-based nonprofit formed to honor vets and the women who worked in factories and shipyards during the war.

"The freedom you enjoy today ... is because of those gentlemen," Kilfoil said.

Kellers’ son Matthew, who spoke for him on Sunday, said his father was a gunner’s mate third-class on an LCT 539 landing craft — similar to those depicted in the opening scene of the 1998 film "Saving Private Ryan" — that was among the initial waves to land at Omaha Beach.

"He was manning a 20-millimeter machine gun," Matthew Kellers told Newsday.

The enemy machine guns on the bluffs "were 75 to 88 millimeter cannonballs," he added. "Three of them pierced the ship from one side, right out the other. And miraculously, he survived."

He said his father seldom spoke about the war until 2009, when he took a trip back to Normandy to receive the Chevalier Legion of Honor from then-French President Nicolas Sarkozy at a ceremony attended by former President Barack Obama.

"The French media and students were asking him questions — that’s when it all came out," Matthew Kellers said. "He must have been suppressing it all that time."

After the war, Kellers married his wife, Barbara, with whom he raised Matthew and two sisters, Valerie and Karen, until Barbara died at age 48. Kellers, who never remarried, worked as a technician at the Long Island Lighting Company and later as an administrator at the Shoreham Nuclear Power Station, which was completed in the 1980s but never opened amid public opposition and environmental concerns.

Matthew Kellers, of East Patchogue, said his father lives close by and enjoys spending time with his four great-grandchildren.

Eric Wieboldt, a volunteer with the veterans group Honor Flight, closed out the ceremony with a rendition of a song he wrote in honor of veterans.

"Welcome my brother, welcome home my friend ... I pray someday, your heartache will end."