Massachusetts Sen. John Kerry (search) is banking on his record of service in Vietnam during the presidential campaign, appearing publicly with former crewmates from the swift boat under his command in Vietnam.

But now, an organization calling itself Swift Boat Veterans for Truth (search) is running an ad aimed at discrediting Kerry's military record.

Leading this group is Vietnam veteran John O'Neill (search), who has also written a soon-to-be-released book entitled, "Unfit for Command." The book will attempt to raise questions about the circumstances surrounding Kerry's Bronze Star citation — and one of Kerry's three Purple Hearts. Last May at a Washington press conference, O'Neill joined other veterans in attacking Kerry's combat record.

"We believe, based upon our experience with him, that he is totally unfit to be commander in chief," said O'Neill, who has been on record criticizing Kerry's military service since the early 1970s.

The Kerry campaign released a substantial pile of documents aimed at discrediting the Swift Boat Veterans, and insists that none of the vets in the ad served directly under Kerry's command.

Click on the box near the top of the story to watch a report by FOX News' Brian Wilson.