Andrew Davies of the Australian Strategic Policy Institute was commenting on a speech by Minister for Defence Materiel Jason Clare at the Submarine Institute of Australia conference now under way in Canberra.

While he stopped short of endorsing Mr Clare's assertion ''submarines are our most important strategic defence asset'', Mr Davies said the minister's enthusiasm indicated the government favoured ''the ambitious end of the spectrum of (future submarine) possibilities''.

ASPI has previously costed 12 locally designed and built future submarines, as set out in the 2009 defence paper, at more than $36 billion, the equivalent of the national broadband network.

Mr Clare said the future submarine would be the largest and most complex defence undertaking in Australian history, and that by the time the last of the 12 vessels had been built the first off the production line would need to be replaced. The government was preparing the groundwork for an industry that could last 100 years or more.

He likened it to the Snowy Mountains scheme and reaffirmed that nuclear submarines, floated as a possibility by former defence minister Joel Fitzgibbon earlier in the week, were not under consideration.

''The US has never exported or leased a naval nuclear reactor,'' he said. ''Acquiring nuclear submarines would therefore involve outsourcing the construction, maintenance and sustainment of the submarines to another country. Tens of billions of dollars that could be invested in Australia (would be) spent overseas.''

Chief of Navy Vice-Admiral Ray Griggs agreed, saying the nuclear debate was a distraction. ''What we must have is a sovereign (submarine) capability, one that we have control over and one that we can support, evolve, adapt and upgrade,'' he said.

Mr Clare said the long awaited future submarine industry skills plan would be finalised by next month and decisions about the ''form, function and location'' of a land-based test site for submarine propulsion would be made in the next 12 months.

Mr Davies said neither development was unexpected and the statements were consistent with previous announcements.

The main piece of good news was that a number of speakers have expressed growing confidence in extending the life of the Collins-class boats until replacements are available.

''There is a consensus, from the life extension evaluation, the Collins could be put through one more duty cycle,'' Mr Davies said. ''That is effectively a life extension of eight to 10 years.'' It is understood HMAS Collins would be the first to have her hull cut open so the diesels and generators could be accessed.