The September 2021 announcement of Australia’s transition to nuclear-powered attack submarines (SSNs) under the AUKUS program indicated that ‘at least eight’ would be acquired. More recently, the rhetoric has firmed up to eight, with the program director telling a Senate committee in May that there would be three Virginia-class SSNs and five AUKUS SSNs. Vice Admiral Jonathan Mead implied that this was the full extent of the program and that decisions for what followed would be left for a future government.

A decision to stop at eight overlooks critical strategic, industrial and personnel considerations that determine the number of submarines Australia acquires.

Since the 2009 defence white paper, successive reviews have affirmed the need for 12 submarines supported by a base on each coast providing specialised infrastructure, workshops and a submarine squadron staff. While nuclear propulsion provides much greater mobility, a submarine can only be in one place at a time. Once its position is revealed by counter-detection or its own offensive actions, uncertainty over its location is removed and with that, its deterrent value diminishes for a period. Added to the reality of our geography, a force able to deploy at least two submarines on each coast would require at least 12 SSNs to provide ongoing uncertainty (for an adversary) and, if needed, operational impact.

It takes three to four submarines to guarantee having one available for deployment. The ‘rule of three’ was validated by the Coles review, but that doesn’t include any spare capacity to cope with unexpected defects. The UK and French experiences confirm that four nuclear-powered ballistic missile submarines (SSBNs) are required to sustain one at sea—noting that SSBNs operate in a much lower mechanical and operationally stressed environment than SSNs.

Industrial issues are significant factors in the cost of ownership and effectiveness of the force. Australia intends to build the AUKUS SSNs in Adelaide. That is thoroughly commendable, but we should expect delays and difficulties as we learn how to do it. In all shipbuilding programs, the time and cost of successive vessels reduces as the workforce and processes are optimised. Typically, based on Australian (and global) experience, the third submarine will cost some 40% less than the first, with much smaller reductions anticipated as later submarines are built.

This only works if the building program is continuous. Stop–start shipbuilding is a well-known recipe for prolonged delays and grossly inflated costs, as demonstrated by Britain’s Astute class, which, according to a House of Commons Defence Committee report in early 2010, was already by then 57 months late and 53% over budget.

Once we have mastered the complexities of building SSNs, as I am sure we will, we shouldn’t stop building.

Australia is planning on a three-year interval between delivery of submarines, driven by the time it will take to generate a crew from our small submarine personnel base and limited sea training capacity in operational Collins-class and US and UK submarines.

Construction of the first submarine will take longer and reduce to a steady state after three or four are built and the workforce has made its way up the learning curve and processes have been optimised. The building process is a production line—at any time, submarines will be in different states of completeness. Construction time doesn’t determine the drumbeat for delivery; rather, construction starts in sufficient time to achieve the delivery drumbeat.

Three years is a slow drumbeat industrially. Shorter would be more efficient but is currently not feasible because of personnel limitations. The personnel training limitation should ease once Australia has at least six SSNs at sea. The drumbeat could then be shortened. A slow drumbeat is more expensive due to idle production but is also likely to contribute to a loss of skilled workers; witness the UK’s experience at Barrow in Furness because of the slow Astute drumbeat.

A construction program building eight submarines at a three-year drumbeat would take 21 years. Submarines typically have a hull life of 25–30 years. Thus, this production line would have nothing to build for four to nine years, and would then be then back into stop–start shipbuilding.

A force of 10 SSNs at a three-year drumbeat with a planned 27-year life is the minimum to provide a continuous-build program, avoiding the stop–start situation. A force of 12 could achieve a shorter drumbeat in the later stages when the personnel restrictions are not so severe.

Decisions on the final size of the force must be made now, at the program’s inception. They drive industrial issues such as the size of facilities, production-line technology, the supply chains supporting the force and the ordering of long lead items such as the reactor. The decision cannot responsibly be left for a future government.

My study of British, French and US submarine-crewing policies, summarised in my 2018 ASPI report, concluded that a force of 10 SSNs with 10 crews was essential to generate the minimum critical mass of experienced personnel. A smaller force will not generate sufficient highly experienced personnel to oversee the safe technical and operational aspects of the program. That calculation assumed one base and one submarine squadron. Two-ocean basing with an additional 200 highly experienced squadron staff, a key link in the operational and safety chain, would require at least 12 SSNs.

Britain’s Royal Navy has six or seven SSNs and four SSBNs operating from one base in a single squadron. Its personnel situation is dire. High wastage rates and shortfalls in many critical categories have reportedly necessitated drafting non-volunteers to submarine training and cannibalising parts and crew to get even one submarine to sea. At times, the RN is unable to achieve even one. Is that where Australia is heading?

The issues are undoubtedly more complex than simply the size of the force, but it reinforces the point that a force of eight SSNs requiring six to seven crews is below critical mass, vulnerable to personnel shortfalls, will struggle to sustain two SSNs deployed, and won’t be able to sustain two-ocean basing.

Even more problematic is whether Australia can achieve an operational, sustainable and deployable SSN capability from eight boats made up of a mix of Virginia and AUKUS designs. The mix of classes adds to the complexity, cost and risk because it entails two supply chains and differing major onboard equipment, spares, and training systems and simulators.

Australia requires at least 12 SSNs to sustain two-ocean basing with two deployable on each coast in the good times. A force of 18—nine on each coast—would be more resilient, reliably providing two deployable SSNs, with three available in the good times.

Eight is plainly insufficient on all counts.

Leaving the decision for a later government will mean greater expense and increase the risk that the program doesn’t produce the needed strategic capability, while stripping funds from other key defence capabilities. A lack of decision, along with Australia’s failure to join the AUKUS SSN initial design effort, indicates inadequate commitment.

A ‘damn the torpedoes’ transition to SSNs could leave us with no submarine capability.

If Australia is not prepared to, or cannot, invest the resources to achieve a viable SSN force, we are better off not continuing down this path.