The Australian Defence Department's Future Submarine Project (SEA 1000), envisions a vessel larger and more capable than the current Collins Class submarines. Political considerations would favour construction of the submarines in Australia. However, the Collins class submarines proved beyond the capabilities of Australian industry and a larger more complex conventional submarine may be beyond the capabilities of even an experienced overseas shipyard. The only technically viable option to meet the requirements as currently set down would be a nuclear powered submarine from an established US or European manufacturer. However, nuclear power would create considerable domestic and international political controversy for Australia. Also it would be difficult for the Australian navy to recruit, train and pay for the large crew needed for nuclear submarine.
One alternative would be to build two different classes of submarine to less demanding requirement. The first would be an enhanced Collins class submarine and the second a smaller overseas procured vessel.
The Collins class submarines suffered problems with engines and electronic systems. In comparison the Australian made hull of the ships was relatively successful. The ships have had limited service and so could be refitted with new sensors, engines and batteries. This would provide local works and a relatively low risk interim vessel. As an example of a relatively low risk upgrade, new lithium batteries could be fitted in place of lead acid batteries, suing similar technology to that of electric cars.
At the same time the Collins class vessels are being refitted in Australia, a new class of vessel based on a proven overseas design could be ordered from a proven overseas shipyard. The standard weapons fit of the submarines would be reduced to increase their range and allow accommodation for special forces. Four of the the six large torpedo tubes would be replaced with smaller tubes suited to self defence, limited warfare against smaller ships, but still capable of disabling large surface combatants.