A 26-year-old New Hampshire man is being remembered as a “courageous individual who made the ultimate sacrifice” days after he and four other Marines died when a military helicopter went down in the mountains outside San Diego.

The Marine Corps on Friday identified Jack Casey, of Dover, as one of the Marines who died in what officials described as a “routine military helicopter training flight” outside San Diego during a “historic storm.”

Casey, a CH-53E helicopter pilot, graduated from St. Thomas Aquinas High School, a private Catholic school in Dover, in 2015 and commissioned into the Marines in May 2019. He then earned a promotion to captain last September, also being awarded a National Defense Service Medal during his service.

Officials at St. Mary Academy of Dover, a private K-8 Catholic school, of which Casey graduated from in 2011, honored their former student on social media Friday.

“It is with heavy hearts that we inform our community of the passing of one of our former students, Jack Casey, while bravely serving our country as a member of the United States Marines,” the school posted on Facebook. “Jack was not only a dedicated student during his time with us but also a courageous individual who made the ultimate sacrifice in defense of our nation’s freedoms. Jack’s unwavering commitment to service and bravery exemplifies the values we hold dear in our community.”

A photo in the post shows Casey as a youngster smiling, wearing a school basketball uniform, and another of him later on instructing children.

The Marines identified the four other troops as Lance Cpl. Donovan Davis, 21, of Kansas; Capt. Miguel Nava, 28, of Michigan; Alec Langen, 23, of Arizona; and Capt. Benjamin Moulton, 27, of Idaho.

New Hampshire Gov. Chris Sununu, in a statement, directed all flags on public buildings and grounds in the Granite State to fly at half-staff.

“Capt. Jack Casey gave his life while serving his country,” Sununu said. “Capt. Jack Casey’s death is a profound loss for his family, his community, New Hampshire, and the country.”

Military officials confirmed Thursday that all five Marines were killed when their helicopter went down during stormy weather, and efforts were underway to recover their remains, which will take weeks because of the rough terrain and weather, said Col. James C. Ford, operations officer with 3rd Marine Aircraft Wing. In the meantime, Marines are staying with the remains round-the-clock to adhere to their ethos of never leaving any Marine behind.

The decorated Marines were assigned to Marine Heavy Helicopter Squadron 361, Marine Aircraft Group 16, 3rd Marine Aircraft Wing and were based at Marine Corps Air Station Miramar in San Diego.

The Marines were flying Tuesday night from Creech Air Force Base, northwest of Las Vegas, where they had been doing unit-level training and were returning home to Miramar, defense officials said.

“We have been confronted with a tragedy that is every service family’s worst fear,” said Lt. Col. Nicholas J. Harvey, commanding officer of the squadron. “The Flying Tigers family stands strong and includes the friends and community who have supported our squadron during this challenging time. We will get through this together.”

The CH-53E Super Stallion helicopter — the largest helicopter in the military, designed to fly in harsh conditions — had gone missing as a storm dumped heavy snow and record rain over California.

Civilian authorities searching on ground and by air located the aircraft just after 9 a.m. Wednesday near the mountain community of Pine Valley, about a 45-mile drive from San Diego, but snowy conditions made it challenging to gain access on the ground, officials said.

President Biden offered his condolences in a statement Thursday.

“Our service members represent the very best of our nation—and these five Marines were no exception,” he said. “Today, as we mourn this profound loss, we honor their selfless service and ultimate sacrifice—and reaffirm the sacred obligation we bear to all those who wear the uniform and their families.”

Casey attended Virginia Military Institute, where he majored in physics and served as Company I commander as a senior in the 2018-19 academic year. Classmate, Capt. Eli Facemire, remembered what Casey meant to the institute in a post on its website Friday afternoon, describing the death as a “jarring loss.”

“Jack was absolutely loved by our class, and all our brother rats knew that Jack loved them,” Facemire wrote. “He bought in fully to his relationships and opportunities, setting an example of friendship and leadership that was looked up to not only by members of the lower classes, but also by his brother rats. His charisma and humility shined through in all he did, and his infectious, fun-loving attitude made him a tremendous joy to simply be around.”

The Associated Press contributed to this report