The navy's new amphibious transport HMAS Choules has returned to Sydney to repair a mechanical fault that cut engine power in half.
HMAS Choules, acquired second-hand from the United Kingdom and assessed as being in very good condition, left Sydney on June 13 to participate in Exercise Hamel.
Just a day later, a defect occurred on one of the six transformers which form part of the ship's propulsion system, reducing propulsion power by 50 per cent.
Defence said the ship's commanding officer made the safe and prudent decision to return to Sydney for repairs.
It said the navy had been advised by the ship's previous operator, the Royal Fleet Auxiliary, that this type of defect was very unusual.
Navy fleet commander Rear Admiral Tim Barrett said a technical investigation into the possible cause had begun.
"Navy and the Defence Materiel Organisation are working extremely closely with the original manufacturer of the transformer to have it repaired and the ship return to sea as soon as possible," a defence statement said.
The 16,000 tonne vessel was built in the UK and served with Britain's Royal Fleet Auxiliary from 2006 until 2011 when she was declared surplus and sold to Australia for $100 million.
She was acquired to provide the navy with an additional amphibious transport capability following early retirement of the landing ships HMAS Manoora and HMAS Kanimbla.
Opposition defence spokesman David Johnston said HMAS Choules was purchased to fill the gaping hole left in the amphibious ship fleet because of problems with HMAS Tobruk, HMAS Sirius and HMAS Success.
"This government has hardly painted itself in glory with the management of its amphibious fleet," he said in a statement.
"We are now facing the lowest level of funding in Defence since 1938 so I am not inspired with confidence that this is going to get better any time soon."
Senator Johnston said HMAS Tobruk had cost $65 million over the past three years with little or no capability to show for it.
HMAS Sirius had been in planned maintenance for most of this year and HMAS Success had not been operational since December 2010 with $86 million spent on rectifying its problems.
"The defence minister must be hoping against hope against another cyclone in the near future because we simply don't have the amphibious capability available to deploy and assist," Senator Johnston said.