THE federal government has been told to explain why two state-of-the-art, $1.5 billion warships have been anchored and inoperable in Sydney Harbour for a month.

The Daily Telegraph yesterday revealed experts have been investigating the HMAS Canberra and HMAS Adelaide for more than a month trying to figure out why they do not work, with the viscosity of the oil in the ships’ engines being part of the investigation.

Yesterday, Vice Admiral Ray Griggs said it was “an engineering problem which we’ve declared,” and dismissed that the problem was as simple as the wrong fuel.

media_camera HMAS Canberra and HMAS Adelaide have been stranded in Sydney Harbour for a month. Picture: Gregg Porteous

“We’re still trying to determine the exact cause of the problem, and there’s a lot of people working on the issue,” he said.

Defence expert Dr Andrew Davies from the Australian Strategic Policy Institute said: “They have 54,000 tonnes of shipping sitting there hoping nobody will notice.

“I am flummoxed why the Navy or government don’t tell us what is going on. Unfortunately a lack of transparency is all too common.”

media_camera Engineers are still trying to determine what has grounded the billion dollar warships. Picture: Supplied/LSIS Sarah Williams media_camera The viscosity of the oil in the ships’ engines is one part of the investigation. Picture: Supplied/ABIS Steven Thomson

Navy sources have confirmed that its own engineers and experts from the Spanish manufacturer are trying to work out what is wrong with the ship’s hi-tech azimuth propulsion systems.

They could not rule out the possibility the wrong oil had been used, the engines had been driven too hard or there was a problem with their manufacture.

Defence Minister Marise Payne has offered no explanation as to what has stranded the two giant helicopter landing vessels at Garden ­Island.