Newly appointed Defence Minister Stephen Smith admits he would have preferred to remain foreign minister but took "very seriously" the right of the prime minister to choose her cabinet.
Prime Minister Julia Gillard confirmed overnight that former prime minister Kevin Rudd was to replace Mr Smith as foreign affairs minister in the new Julia Gillard government.
Ms Gillard was expected to announce her new cabinet later on Saturday.
At a press conference in Perth, Mr Smith, Labor's third defence minister in three years, said he was undertaking a "a heavy burden, a heavy obligation" as defence minister.
He said the deaths of Australian soldiers in Afghanistan had weighed heavily on former Defence Minister John Faulkner "as it does on any defence minister".
He said he had it made it clear to the prime minister "from the first moment" that she was to form a cabinet, "that I was in her hands and at her disposal".
'Worked well with Rudd'
Mr Smith said he had worked very well with Mr Rudd, when he was prime minister.
"You can never have a crack of light between a foreign minister and a prime minister and that has been the approach I have assiduously adopted whether my prime minister was Mr Rudd or my prime minister was Julia Gillard."
Mr Smith said he had talked to Mr Rudd in the caucus room last week.
"I was keen to make sure he was fit and well after his recent operation and he was keen to make sure I was in good spirits," Mr Smith said.
"We are professional colleagues and we wished each other well."
Mr Smith said that when Ms Gillard asked him which portfolio he wanted, he had told her: "I was very happy to continue with foreign affairs", but he accepted it was her decision to appoint Mr Rudd to that role.
"The prime minister asked me what I would like to do and I said defence," he said.
Role a 'heavy burden'
Mr Smith said he would work very hard to discharge what he considered to be a "heavy burden", being responsible for Australians serving and dying in dangerous conditions overseas.
He said he was looking forward to a forthcoming parliamentary debate on Afghanistan.
He said Australians would always ask questions about the value of the Afghanistan commitment when Australian soldiers continued to be killed there.
"But on a day like September 11 Australians will be reminded that there are terrible consequences for Australians if international terrorism is allowed to run free," he said.
Mr Smith said Australia had always made it clear it had an enduring commitment to Afghanistan.
