BOSTON >> An unmanned submarine has recorded some of the most detailed images of two American ships that sank off the coast of England during World War II, according to the Massachusetts company that surveyed the wreckage to mark the disaster’s 70th anniversary.

Bourne, Mass.-based Hydroid says they are the first high-definition sonar images of two ships sunk by German forces during Exercise Tiger, a rehearsal for the D-Day invasion. The torpedo attack on April 28, 1944, claimed the lives of 749 U.S. soldiers and sailors.

Richard “Bungy” Williams, a regional manager for Hydroid Europe, said the company was interested in exploring the area because of the upcoming anniversary of the attack. He said the images will be donated to the United Kingdom’s National Archive and local memorials.

The autonomous undersea vehicle recorded images of the two boats about 50 meters beneath the surface of the English Channel. Williams said divers have accessed the site before, but the submarine provided the highest quality images yet, including one showing a boat’s upturned stern.

“Using the AUV we could get down very close to the wreck,” he said. Hydroid, a subsidiary of Kongsberg Maritime, manufactures the vehicles.

The casualties from Exercise Tiger were one of the least known Allied disasters of World War II. Fast-moving German torpedo boats happened upon the convoy, sank two ships and badly damaged a third during the practice run for the invasion.

The survivors were warned to keep it secret, and the casualties were not announced until nearly two months after the Normandy invasion. Full details were not known until 1974, when the records were declassified.

An annual wreath-laying to honor the victims is scheduled for Monday at U.S. Coast Guard Station Barnegat Light in New Jersey.