HMAS Adelaide has been dry-docked as engineers scramble to fix issues from just 18 months in service.

One of the Royal Australian Navy's largest warships is having problems with its Landing Helicopter Dock (LHD), which was commissioned into service just 18 months ago, and is now out of action at Sydney's Garden Island Naval base.

HMAS Adelaide's sister ship HMAS Canberra is there for repairs as well.

“You don't expect it when it's a few years old. This is capability that we should be confident that we got the specifications right and it should be operational,” David Smith from Professionals Australia, a union representing Defence scientists and engineers, told reporters this week.

“It's incredibly significant given the billions of dollars we're investing in naval capability.”

The Defence Department has not said much.

“During first-of-class flight trials, Defence identified an emergent issue with the propulsion systems of HMAS Canberra. HMAS Adelaide was also inspected and there are indications of a similar issue,” Defence said in a statement.

“Defence has adopted a deliberate and disciplined approach to resolve this problem early in the ships' life.”

Defence Minister Marise Payne expressed frustration at the delay in fixing the Navy's two largest ships.

“This is the period of time in which, in Defence acquisition and implementation terms, we've identified these sorts of issues and we address them,” she said.

“That's not to say that it's not frustrating that it has been an issue that's under examination for some time.”

There is speculation that neither of the ship’s engine issues will be fixed before next month's Talisman Sabre military exercises with the United States.

“Whatever time that takes is frankly the time that it will take. I don't intend to ask them to rush it, I don't intend them to work to an artificial or self-imposed deadline from anyone else,” Ms Payne said.

Labor has called on the Government reveal exactly what is wrong.