A Vietnam War veteran has launched a defamation case in a South Australian court over accusations that he fabricated large parts of his service record.

RSL South Australia director Tony Flaherty was labelled a "valour thief" on an anonymous website, which claims to expose hundreds of military frauds.

The 73-year-old is suing the man he claims reported him, and is also in mediation with the RSL's South Australian branch.

He's among scores of veterans who complain the site has unfairly ruined their reputations.