Ballard said the wreck, which was found in May, will be left where it is.

"We have an understanding with the Kennedy family as well as others who lost loved ones — there were two people lost from the boat — that we will not disturb the site and we will not dig it up," he said.

Eventually, the site might become part of Ballard's planned network of underwater museums accessible over the Internet. But he said it would probably be years before that happens, given the technology required.

PT-109 was rammed early on the morning of Aug. 2, 1943. The destroyer was believed to have struck Kennedy's 80-foot boat amidship, slicing it in two. But Ballard said it appears PT-109 was actually struck a glancing blow that sheared off only a portion of the stern.

The 11 surviving crewmen clung to the slowly sinking bow, then swam to a small island. Kennedy towed an injured crewman to shore by swimming with a strap from the man's lifejacket in his teeth.

The future president was awarded the Navy and Marine Corps Medal and a Purple Heart. The episode was dramatized in a 1963 movie.

Ballard, who has also explored such shipwrecks as the Bismarck, the Lusitania and the Yorktown, searched the bottom of the sea with a remotely operated vehicle and found a loaded torpedo tube and a few pieces of gear jutting from the sand.

The torpedo and launching tube are exact matches for equipment used only on PT boats until 1944, a Naval Historical Center expert said.

"A check of Navy records indicates that no other PT-type vessels were lost in this location," the Navy said in a statement. "This information combined with the physical evidence suggests that this is likely the wreck of the PT-109."

Sen. Edward Kennedy , D-Mass., said Ballard and the National Geographic  Society should be commended for the research.