Normally I would not justify such slanderous attacks with a response, but I thought this article was worth mentioning :

Republican Sen. John McCain, a former prisoner of war in Vietnam, called an ad criticizing John Kerry's military service "dishonest and dishonorable" and urged the White House on Thursday to condemn it as well.

...

The leader of the group, retired Adm. Roy Hoffmann, said none of the 13 veterans in the commercial served on Kerry's boat but rather were in other swiftboats within 50 yards of Kerry's.

Jim Rassmann, an Army veteran who was saved by Kerry, said there were only six crewmates who served with Kerry on his boat. Five support his candidacy and one is deceased.