Australia's future submarines program is on track, despite concerns raised in an audit report, Prime Minister Scott Morrison says.
The Australian National Audit Office found in a review of the $80 billion submarine program two key contract milestones had been extended.
"As a result, Defence cannot demonstrate that its expenditure of $396 million on design of the future submarine has been fully effective," the audit office said.
The design and construction of the submarines is the largest Defence procurement in Australia's history.
Defence is in the process of acquiring 12 new submarines to replace six Collins Class vessels, the first of which is due to be delivered in 2032.
Mr Morrison said the audit report had confirmed there had been no change to the delivery timeframe or the budget and getting the design right in the early stages would save money down the track.
"Defence has advised delays to design milestones will be recovered by the next milestone in January 2021," he told reporters in Canberra on Wednesday.
"The government is working to ensure we keep the project on track, as it is.
"It's a big task, it's a hard task, it's a challenging task, but we have the best people working on it to get the job done."