By March next year, Richard Marles expects to know when the submarines secured by the former Morrison government under the AUKUS partnership will be operational.
But first it's important to understand what submarines will be secured, where Australia's defence capability gaps are and how they can be filled, he said.
"What we were left with by the former government was a real mess in this area and the solution to that mess is answering each of those questions," he told ABC radio on Wednesday.
"We need to look at options of bringing all of that forward ... (and) how we can get that submarine in service sooner rather than later."
Defence heads previously told government officials there was an aim to have at least one nuclear-powered submarine in the water by 2040.
The defence minister is reviewing whether to go with a United States or United Kingdom submarine plan, with the 18-month assessment due in March 2023.
Part of the review includes bringing forward the time frame that submarines could be delivered, and stemming from that, what capability gaps would arise.
But Australia's likelihood of having a nuclear-powered submarine in operation as early as 2030 is unlikely, the defence minister believes.
"That is optimistic in the extreme," he said.
"We will be looking at every option available to try and bring that time frame forward. I think bringing it forward to eight years from now would be extremely optimistic."
Mr Marles also defended his decision to extend General Angus Campbell's term by an additional two years despite criticism of the defence chief's ability to deliver on capability.
"It's not (defence heads) who oversaw the issues and the problems that we now face, it was the former government," he said.
"The former government's handling of national security ... specifically the procurement of their submarines was one of the worst failures in defence procurement that we have seen in our history."
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