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The USS Emmons served the United States proudly through World War II, right up until April 6, 1945, when it was attacked by five kamikaze pilots off the coast of Okinawa. One day later, the U.S. Navy sank the destroyer to prevent it from falling into the hands of the Japanese.

The bodies of 60 American sailors went down with the ship.

For 65 years, the Emmons lay peacefully on the ocean floor, guns raised skyward -- until recently, when divers discovered that the ship had been vandalized. Its builder’s plaque -- the metal plate and vessel’s “birth certificate” -- had been removed.

To veterans, it's like robbing a grave. Unknown thieves dived down to the ship and looted it, making off with its most precious commodity – honor.

A ship’s “data plaque” was usually a brass plate cast or embossed with information on the ship's significant dates and builder,” Warman’s Guide to WWII Collectibles author John Graf told FoxNews.com. "Usually, there would be just one made for each ship, so each example tends to be unique and command collector interest.”

"Naturally, we’re very upset because we feel that it's ours, it's our ship," said Ed Hoffman, 85, one of the handful of the Emmons' original crew members – "one of the young ones," he says.

"There were six of us in the pilot house; only two of us got out," Hoffman recalled in an interview with FoxNews.com.

“That ship is a resting place,” another survivor, 92 year-old Harold Jay, told FoxNews.com.  “Those men deserve our respect.” 

There are plenty of theories on who would vandalize a naval grave. But at this point, nobody really knows who's responsible.

“It may have been Japanese authorities,” said military historian Martin Morgan. "Japanese have become more interested in interacting with their history of the Second World War, and unfortunately Japanese historians have participated in distortions of the political and historical record of World War II."

And recently, anti-U.S. military presence has become more visible. In the spring, nearly 100,000 Japanese protested the presence of U.S. military forces on Okinawa, raising the possibility that locals secretly dived to the sunken ship.

But Hoffman isn't buying that theory. "Chances are it's not native divers,” he said. “They have a great sensibility for the resting place of the dead."

Tamio Ota, a still photographer in Okinawa, agrees.  “Okinawans are sensitive to the dead.  We believe in ancestry worship here in Okinawa; we respect the dead from both sides.” Ota said.

The U.S. Navy retains custody of its ship and aircraft wrecks despite the passage of time and regardless of where they are lost – whether in U.S., foreign or international waters -- but it said there is some question as to who should or even could investigate the theft of the Emmons plaque.

"We're a felony investigative agency," Naval Criminal Investigative Service spokesman Ed Buice told FoxNews.com.  News of the the Emmons vandalism has naval authorities puzzled.

“In my years at NCIS, I’ve never heard of something like this,” Buice said.

Graf suspects souvenir hunters are responsible.

“Anything associated with WWII U.S. Navy vessels are collectible,” he told FoxNews.com via e-mail. "Anything associated with U.S. Navy vessels that were in combat and sustain damage or even sunk are very collectible and command higher prices.”

The idea of a souvenir collector stealing from the USS Emmons site is disturbing to many -- “All military people know what a sunken ship means,” Ota said -- but the Emmons has become a destination dive for international tourists, and collectors know a valuable "souvenir" when they see one. Whoever removed the ship's plaque likely had some knowledge of its worth, said Graf.

The looting of the Emmons is a blow for the ship's survivors and their families, who have pledged to honor their loved ones' service.  Members of the USS Emmons Association, which recently established a college scholarship to interest young people in the ship's history, say it will be hard to put this incident behind them.

“The USS Emmons was more than the veterans' temporary home. It is the special connection to their love of and contribution to America,” Jay's daughter, Pepper Jay, told FoxNews.com.

She said the plaque "bestowed honor on their ship and fallen shipmates. When it went missing, the survivors felt that part of themselves had also gone missing.”