Lack of government transparency around the $50 billion future submarines program has led the public to doubt its authenticity, says former federal opposition leader John Hewson.
Dr Hewson, leader of the Liberal Party between 1990-1994, says the public has been given mixed messages about where the submarine construction would be carried out.
With initial suggestions up to 90 per cent of the work could be done in SA but then indications more than a third would be carried out overseas, the situation was confusing, Dr Hewson said.
"I think those sort of differences in the message are very important and they cause people to doubt the authenticity of the project itself."
Defence Industry Minister Christopher Pyne has said at least 60 per cent of the build will be carried out locally - the minimum for a project to be defined as a local build.
But Sean Costello, the former local boss of French designer Naval Group, had in 2016 flagged that figure would be 90 per cent.
His successor, interim chief Brent Clark, would not recommit on that target before a Senate committee last year.
Dr Hewson said transparency in defence procurement had been an issue over many years.
"People need to know the detail," he said.
"You can't pretend that you shouldn't have to provide that or that it's commercial-in-confidence because, quite frankly, that's nonsense."
The first of the fleet of 12 submarines, which will replace the ageing Collins-class vessels, is due to enter service in the early 2030s.
Mr Pyne has said the program is expected to generate an annual average of 2800 jobs during its lifetime.