OLD SAYBROOK, Conn. (WTNH) — A maritime mystery dating back almost 80 years has been solved.

Divers in Connecticut say they have finally found the wreck of The Defender, an experimental submarine that sank in Long Island Sound in 1946. The 92-foot-long (28-meter-long) boat was found Sunday by a team led by Richard Simon, a commercial diver from Coventry, Connecticut.

Under the surface of Long Island Sound, there are mysteries, and divers like Simon, with Shoreline Diving, love finding them.

“As a kid, I grew up diving in Long Island Sound,” Simon said. “As a diver, it was one of those myths, ‘Hey, there’s a submarine lost in Long Island Sound.'”

General Dynamics Electric Boat is a well-known shipbuilder, but more than 100 years ago, there was another submarine maker. A millionaire inventor in Milford named Simon Lake, with his Bridgeport-based Lake Torpedo Boat Company, built a prototype called The Defender, originally named the Lake.

He had hoped to win a competition for a U.S. Navy contract, according to NavSource Online, a website dedicated to preserving naval history.

“So, in 1907, he built the submarine Defender to sell it to the Navy,” Simon said. “You know, it has wheels, it can drive on the bottom, you can launch divers from it. Pretty revolutionary for its time. And the Navy said, ‘This is a little too new for us.'”

Lake tried for years to get the government interested in his submarine, with no luck. So, the Defender hung around the Connecticut shoreline for decades, getting less and less seaworthy until it sank for good in 1946 somewhere off the coast of Old Saybrook.

Some say it was being towed when it sank, and some say it was scuttled on purpose, but nobody knew exactly where it was until Simon and his friends started looking.

Simon said he had been interested in the story of the Defender for years. He spent months going over known sonar and underwater mapping surveys of the bottom of the sound, as well as government documents obtained under the Freedom of Information Act, to identify any anomaly that fit the size of the sub.

For two years, they narrowed it down with charts and sonar until they thought they had found something the right size and shape.

“A submarine has a very distinct shape,” Simon said. “It needs to be 100 feet long and 13 feet in diameter. So I made a list of everything that was that long and there was one target on that list.”

But it was in deep water.

“It’s in a spot that’s tidal, so you only have about a 45-minute time window when you can actually dive the wreck,” Simon said.

On Sunday, they got down at the right time and found what they were looking for. The size, shape, and age all matched The Defender.

They found it lying on the bottom, more than 150 feet (45 meters) beneath the water’s surface, off the coast of Old Saybrook.

“It was legitimately hiding in plain sight,” he said. “It’s on the charts. It’s known about in Long Island Sound, just no one knew what it was.”

It was the first of many dives he and his crew would do.

“This is kind of a treasure for all of us. We are the submarine capital, if you will, of the world. We have Electric Boat, we have the Navy base,” said Simon. “There’s so much history here with submarines that it’s really an important state of our state history.”

Simon said he would make the exact location public once he finishes documenting the wreck for history.

The Associated Press contributed to this report.