BOSTON -- Divers have discovered a World War II-era German submarine nearly 70 years after it sank under withering U.S. attack in waters off Nantucket.

The U-550 was found Monday by a privately funded group organized by New Jersey lawyer Joe Mazraani. It was the second trip in two years to the site by the team, some of whom had been searching for the lost U-boat for two decades.

Using side-scan sonar, the seven-man team located the wreck listing to its side in deep water about 70 miles south of Nantucket.

Sonar operator Garry Kozak said he spotted the 252-foot submarine during the second of an exhausting two days of searching. Kozak said the team asked him if they'd found it, then erupted in joy without a word from him.

"They could see it with the grin (on my face) and the look in my eyes," Kozak said.

On April 16, 1944, the U-550 torpedoed the gasoline tanker SS Pan Pennsylvania, which had lagged behind its protective convoy as it set out with 140,000 barrels of gasoline for Great Britain, according to the U.S. Coast Guard website and research by Mazraani.

The U-boat slipped under the doomed tanker to hide. But one of the tanker's three escorts, the USS Joyce, saw it on sonar and severely damaged it by dropping depth charges.

The Germans, forced to surface, manned their deck guns while another escort vessel, the USS Gandy, returned fire and rammed the U-boat. The third escort, the USS Peterson, then hit the U-boat with two more depth charges. The crew abandoned the submarine, but not before setting off explosions to scuttle it. The submarine hadn't been seen again until Monday.

The U-550 is one of several World War II-era German U-boats that have been discovered off the U.S. coast, but it's the only one that sank in that area, Mazraani said. He said it's been tough to find largely because military positioning of the battle was imprecise, and searchers had only a general idea where the submarine was when it sank. Kozak noted that the site is far offshore and has only limited windows of good weather.

The team towed a side-scan sonar vessel in a mow-the-lawn pattern over the search area and found the U-550 after covering 100 square miles of ocean, between the trip this year and last year, Kozak said.

Just the nose of U-boat was visible on sonar on the first pass, but the team was delirious after the second pass, when the sonar image made it obvious they'd found it, Mazraani said. Quick dives to the wreck to beat bad weather confirmed the find with pictures.

The other team members were Steve Gatto, Tom Packer, Brad Sheard, Eric Takakjian and Anthony Tedsechi.

Mazraani is cagey about the vessel's precise location, saying only that it's in deep water. Mazraani's said his best estimate was that the team spent thousands of dollars of its own money on the expedition. He joked that no one on the team, whose members range in age from the mid-20s to mid-50s, stands to make money from the find unless someone writes a book.

Mazraani said the next step is to contact any sailors or their families from the escort vessels, the tanker and the German U-boat to share the news and show the pictures. Another trip to the site is coming, he said, adding the investigation has just started.

"The history behind it all is really what drives us," Mazraani said.