Australia needs to seriously consider moving to a nuclear-powered submarine force because, in the rapidly changing circumstances of the region, it is the best solution to meet the Royal Australian Navy’s demanding strategic and operational requirements. The very long timescales and extraordinarily high and escalating cost of the Attack-class submarine program make this imperative.

The program, with a current price tag of more than $50 billion, won’t produce a single operational submarine until 2036, by which time the threat or the technology may have changed dramatically. The program is still planning to use superseded technology and will leave a significant capability gap. So, is it worth it? Or is there a better, faster, more cost-effective way of getting a similar or superior capability?

A number of arguments have been offered against Australia’s ‘going nuclear’, but they really aren’t the showstoppers they’re often claimed to be.

A fresh approach at both the political and military levels could determine whether attitudes are shifting and new partnerships are possible, especially with the advent of smaller nuclear reactors.

Public support for such a force can be gained if the requirements and benefits are discussed honestly and openly, with total costs and safety issues explained. This will require bipartisan political support.

Australia should consider switching to an existing SSN like the Suffren class made by France’s Naval Group. The Suffrens are the nuclear-powered cousin to the conventionally powered Attack class that the company is building for Australia. They could more readily satisfy the RAN’s needs through a similar or even a shorter procurement process.

An early discussion would be with Naval Group, as shifting to a nuclear strategy would mean significantly modifying the program to build the Attack class.  France is understood to have  already offered the Suffren to the RAN.  Discussions with the US and UK navies would also be advisable, covering nuclear safety, support, training, technology transfer and the like.

The requirement for 12 Attack-class submarines to replace the six Collins-class vessels is based on a need to be able to unilaterally deter and defend against surface or subsurface attacks on the Australian homeland and the Australian Defence Force. The submarines will carry out intelligence-gathering, surveillance, targeting and reconnaissance operations, possibly many thousands of kilometres away from home, in seas that are becoming more challenging and potentially more hostile.

In wartime or periods of tension, the submarines would also be expected to provide area defence and sea denial, with long covert submerged operations, alone or with allies. That could involve interdicting anti-submarine and anti-surface ships, which will require the latest in command, control, communications, sensor and weapon technology.

Even without long transits to the South China Sea, simply providing a continuous presence in the key sea lines of communication and choke points to the north of Australia, requires a substantial submarine force. That’s why the fleet is set to double in size.

Australia’s submarines will be unable to meet the nation’s strategic and tactical requirements for some time, especially in the early years of a transition from the Collins class. This is because of a combination of factors, including the slow rate of construction of new subs, the requirement to substantially increase the number of submariners and train them on new systems, and the need for maintenance, defect rectification, leave and shore time.

Despite the increased numbers, as currently specified the new submarines will still be diesel-powered and fitted with lead–acid batteries. They will not be equipped with air-independent propulsion and will be slow during transit. At best, only half of an 80-day operation will be spent in the designated area of operations. The vessels’ regular need to surface, or ‘snort’, to charge their batteries will also offer unwelcome opportunities for an adversary to locate them.

The decision to work with the French solely on a new diesel–electric, rather than nuclear, design is the main factor that will limit the submarines’ effectiveness. It is also behind the program’s enormous cost, risk and timeframe.

A nuclear power plant provides a submarine with a virtually unlimited supply of electricity, high maximum and sustained submerged transit speeds, an almost endless capability to loiter at low speed, and the ability to escape, evade and move to the area of operations expeditiously, far from base, without any need to surface. These are enormous performance improvements over conventionally powered submarines, especially those that, like the Attack class, aren’t designed to use air-independent propulsion or lithium- or zinc-based batteries.

The complicating factors of a move to nuclear submarines would centre on the political aspects of using nuclear power and the substantial costs involved in providing the personnel, training and support infrastructure required to meet modern nuclear safety standards. Each submarine would also cost more than a conventional equivalent. Given that the current program already looks unlikely to provide any new or enhanced submarine capability until the 2040s, a decision to switch to a partial or full SSN fleet might not entail much, if any, further delay.

There’s already a requirement for an interim capability that includes up to six life-extended Collins boats. A further six ‘son of Collins’ vessels will almost certainly be needed to maintain continuity of operations and provide enough fully trained submariners to be able to crew any future SSNs.

Australia’s lack of a nuclear power industry shouldn’t prevent a move to nuclear-powered submarines, but programs would need to be introduced now, including new physics and technical courses in Defence and in civil educational institutions.

Finding, training and retaining personnel is the potential Achilles heel and requires extensive modelling and a major recruitment drive. This has proved extremely challenging for the Royal Navy, especially in the areas of nuclear watch-keepers and junior executive and engineering branch officers.

The recruitment work already in place provides a good basis for finding submarine crew. More complex and time-consuming would be training enough experienced, qualified nuclear engineers and executive branch officers, and maintaining a critical mass. Initially, Australia would need to use other nations’ facilities for much of this training.

The transition won’t be simple, as some personnel would be trained on current and new conventional submarines, while others would need lengthy nuclear training to prepare for the first SSN. In parallel will come the requirement to recruit, train and certify civilian nuclear engineering, support and scientific personnel to work in naval bases and headquarters.

A major construction program would be required to provide facilities to berth, maintain and repair 10 to 12 SSNs. This would include dry docks and nuclear-certified cranes. There could also be a requirement to refuel. While much of the cost of developing an SSN capability falls in the infrastructure area, the regulations and requirements are well documented and the civil engineering is straightforward. It would provide significant employment opportunities.

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A press briefing on the Australian future submarine (FSM) program by Jean-Michel Billig, the Australian program director for Naval Group (formerly DCNS), at the PACIFIC 2017 international maritime expo a few weeks ago set some hares running. Among other things, he said that ‘The vessels may end up with conventional propellers as well as air independent propulsion, which helps to increase underwater endurance’.

That was significant because DCNS made a big deal of offering Australia pump-jet propulsion during the competitive evaluation process for the FSM. We were told that ‘The Shortfin Barracuda uses a pump-jet propulsor that combines a rotor and stator within a duct to significantly reduce the level of radiated noise [compared with propellers] and avoids cavitation’. And DCNS Australia’s CEO really played up the significance of the technology:

There’s no better example of [the benefits of a strategic Australia–France relationship] than the offer from France to transfer to Australia sovereign control and use of pump-jet propulsion technology for the Shortfin Barracuda—technology resident only in France, the UK and the USA. Technology born from the French SSBN program a generation ago. The stealth and hydrodynamic performances of pump jet propulsion are of course classified and in Australia known only to DCNS and the Australian Government.

While no hard data has made its way into the public domain, an argument began doing the rounds among submarine tragics that pump jets are too inefficient at low speeds to make sense on a conventional submarine. (See here, for example, and I’ve had a stack of correspondence along those lines.) The recent Insight Economics report (PDF) has a chart (p. 103, redrawn below) that seems to show that pump jets turn electrical power into propulsion less efficiently than propellers at low speeds, though they are superior at higher speeds.

Critics of the pump jet argue that diesel-electric submarines spend much of their time at low speed, relying on batteries for power, so a propeller is the natural drive of choice for conventional submarines. That’s probably the basis for recent parliamentary questions (PDF, p. 22) about the submerged endurance of the FSM. Conversely, it’s argued, pump jets are the preferred propulsion system for nuclear submarines that travel at higher speeds and have almost unlimited power from a nuclear reactor.

I’m always wary of graphs without numbers, so I don’t know how much to read into the figure. But the argument is consistent with the observation that there are nuclear submarines around the world with pump jets (including the new French boats), but all conventionals have propellers. As I told the ABC recently, experiments with pump jets on diesel-electric boats—such as a single Russian navy Kilo-class submarine—don’t seem to have caught on. So there seems to be at least a prima facie case for propellers.

But an extraordinary claim—in this case that Naval Group is pulling the wool over the eyes of a clueless Commonwealth—requires extraordinary evidence. And on the flip side, Defence doesn’t seem to be too concerned. The department’s succinct response to a recent parliamentary question on notice was that ‘A [pump jet] can provide higher propulsive efficiency across the speed range of a submarine, including the patrol speed of conventional submarines’.

So how can we resolve the apparent discrepancy between propulsion physics (and observation of the world’s submarine fleets) and the statements of Naval Group and Defence? A possible answer is that the case against pump jets focuses on only one part of the story. If all you ever wanted a submarine to do was amble around at low speed, then you’d opt for a propeller. But there are other considerations. For a start, you want the submarine to be as quiet as possible, and the pump jet probably has the edge there. If extra stealth comes without too much performance impact, you’d take it—especially in the future anti-submarine warfare environment.

And Australia’s submarines have long transits to their patrol areas—substantially greater distances than other conventional boats—so efficient propulsion at higher transit speeds would save fuel, giving greater endurance in the patrol area. Reducing transit time is an effective force multiplier: a submarine with a 70-day endurance and a transit speed of 8 knots (representative numbers for a large diesel-electric boat like Collins) will use 31 days (44% of its total endurance) transiting to and from a patrol area 3,000 nautical miles (5,560 kilometres) from base. Reducing transit time and saving fuel potentially have a big payoff.

Another consideration is that the submarine has power requirements other than propulsion. At low speeds, the power usage can be dominated by the ‘hotel load’—the power required for onboard functions like the combat system and air conditioning. That might seem surprising, but the power required for propulsion goes as the cube of the speed—doubling the speed increases power consumption by a factor of eight. I’ve done a few simple calculations (algebra fans can see the geeky annex below), and it turns out that the submerged endurance on patrol at low speed can be many times the submerged endurance at transit speed, even if the drive is less efficient at patrol speed. I had to make a few simplifying assumptions, but a submerged endurance of over a week on batteries alone is entirely plausible, even without air-independent propulsion.

Nothing here proves that the pump-jet solution is right for the FSM, and it still might not work out. Hard numbers on noise and efficiency, including the crossover point of propeller and pump-jet efficiency, are needed for a robust assessment. It’s a safe bet that those won’t become public anytime soon, but that’s what the project office will be looking at when making engineering trade-offs during the design process.

Geeky annex

The power required for mobility at a speed $v$ is defined as $P_M (v)=P(v) epsilon (v)$, where $P(v)$ is the power taken from the batteries and $epsilon (v)$ is the efficiency of the entire drive train, including the propulsor and the main motor. If $P_T (v)$ is the total power being drawn and $P_H $ is the hotel load (assumed constant) then $P_T (v) = P_H + P_M (v)/ epsilon (v)$. Using the cube relationship for motive power as a function of speed, a little algebra shows that the ratio of the power use at transit speed to patrol speed is:

[

frac{P_T (v_T )}{P_T (v_P )}=mu+ frac{epsilon(v_P )}{epsilon(v_T )} (frac{v_T}{v_P})^3 (1-mu),

]

Here $mu = frac{P_H }{P_T (v_P )}$ is the fraction of power consumed by the hotel load in patrol conditions. To get a feel for the numbers involved, if the hotel load is 50% of the patrol power requirement, and the transit speed is four times the patrol speed, then the ratio is a little over eight, even if the propulsion is only 25% as efficient at the lower speed. That means that a day on transit power is equivalent to eight days on patrol from the point of view of total energy consumption.

Australia’s decision to spend $50 billion on 12 French diesel-electric Shortfin Barracuda submarines reflects a long-established government preference for non-nuclear submarine forces. But will this preference remain strategically credible in future years if our strategic circumstances continue to deteriorate and if potential competitors continue to expand and to modernise their submarine fleets?

Australia’s new submarines are a conventional variant of a French nuclear-powered submarine design, and are scheduled to enter service from the early 2030s to the 2050s. So perhaps we need to remain open to possibly acquiring some nuclear-powered Shortfin Barracudas during the lengthy building period. A mix of conventional and nuclear submarines might prove to be an optimum outcome for Australia.

Of course it would be necessary to consider serious questions including cost, capability, crew training and availability, submarine numbers, local access to nuclear technology and nuclear technicians, inter-service rivalries, and domestic political acceptability among other things. But if changing circumstances were to force a decision on government, there’s at least some intriguing fairly recent history to help guide decision-makers.

The history is detailed in the prize-winning The Silent Deep by Peter Hennessy and James Jinks (Penguin Books, 2016), a history of the British Royal Navy submarine service since 1945. Hennessy and Jinks reveal the impact on the Royal Navy of the October 1957 visit to the UK of the USS Nautilus, the world’s first operational nuclear submarine, to take part in Operation Rum Tub, an exercise that matched Nautilus against Royal Navy ships.

In the exercise, Nautilus tore the Royal Navy apart so comprehensively that Lord Louis Mountbatten, the First Sea Lord, was moved to write at the time ‘we now appreciate that we are in the presence of a revolution in naval warfare in some ways more far-reaching than the transition from sail to steam’.

The Commander in Chief Home Fleet, Admiral Sir John Eccles, summed up the four key advantages of the nuclear submarine. It had complete freedom of action in three dimensions, it could disregard threats from the air because it could stay submerged, it had a good picture of what was happening on the surface, and it was ‘vastly superior’ to surface ships and conventional submarines in the attack role.

The Admiralty Board declared: ‘If the Royal Navy did not acquire these submarines it would cease to count as a naval force in world affairs’. It’s worth underscoring that these judgements on nuclear submarines were written 60 years ago.

Hennessy and Jinks detail the saga of Britain’s initial acquisition of four nuclear submarines with what passed for assistance from American Admiral Hyman G. Rickover. They show how the acquisitions transformed Britain’s ability to deliver nuclear weapons from the sea rather than from the air. It’s a remarkable narrative of Cold War strategic evolution.

Given the changing and increasingly fraught strategic environment facing Australia, defence planners cannot sit back contentedly as the new submarine construction gets underway. It may be that conventional submarine technology today is far superior to what was available to the Royal Navy during Operation Rum Tub in 1957. But it is also certain that nuclear submarine technology has advanced since the era of USS Nautilus. Australia needs to remain nimble and flexible in its force structure judgements

A fleet of conventional Shortfin Barracuda submarines would doubtless contribute to Australia’s ability to deter potential foreign intrusions and to support international naval coalitions with allies like the United States and Japan. But Australians would do well to recognise that in regional terms it is a very small fleet indeed.

North Korea, for example, has the region’s biggest submarine fleet with some 70 decrepit old tubs. China has some 68 submarines including around 10 nuclear submarines and it is working ferociously to increase and modernise its fleet. Indonesia has two submarines in service, two under sea trials and one under construction and it’s moving to update and modernise.

Of course these sketchy and imprecise raw numbers mean little. What matters is the quality of the boats and the lethality of their arms. Happily Australia’s key ally, the United States, has far and away the most powerful submarine fleet globally with some 66 boats, all nuclear-powered. What is much less clear is whether the US will remain a fully engaged partner in the Trump and post-Trump eras.

Which is why there may be some sense in noting the lessons of history. Back in 1957, as Hennessy and Jinks argue, the question was not whether the UK could afford nuclear submarines. After Nautilus, the question was whether the UK could afford to be without them. That question might, in time, confront Australia.

Everyone agrees that we should, whenever possible, buy military equipment based closely on existing designs rather than new ones. Doing so results in lower costs, lower risks and quicker delivery. So why aren’t we going for a boat closer to an existing design for the Future Submarine? The key answer is the size of the boat we’re after; no one has an ‘off the shelf’ design for a conventional boat the size we want.

But why do we want such a big boat? There are many views on this. I’ve previously suggested that the key drivers are roles and range: we want our subs to carry a lot of different systems to perform many different roles, and to operate a long way from base.

Some other factors may have come into play as well. The decision early in the process to mandate the US AS/BYG-1 combat management system might well have committed us to a big boat because that system reportedly needs more space and power than existing conventional designs could provide, except for the Collins. And there remains a suggestion that some decision-makers have been influenced by the desire to create a path to a nuclear-powered submarine in the not-too-distant future, which would certainly help explain a preference for a bigger boat.

That all shows that the real reasons the Government has chosen to buy such a big boat remain a mystery, like so much else about the project—the status of AIP, the apparent decision against Li-ion batteries, the choice of pump jet propulsion, the alleged acoustic failings of the German contender and the total absence of any competitive discipline in the process from now on.

If the choice has been driven by the combat system or the dream of a nuclear future, then it’s plainly a huge mistake. Neither of those offers sufficient reason to accept the costs, risks and delays inherent in the current plan. Nor, as I have argued, does the desire for a submarine optimised for operations beyond the core role of anti-ship warfare.

The only good reason to go for a big boat is mission range and endurance. That really is important. Submarines—especially conventionally-powered ones—are most effective when they operate closest to the home ports of a potential adversary or in key chokepoints. For Australian subs operating from HMAS Stirling those are a long way away. (Exactly which ports and chokepoints we’re talking about is a big question, but for another time.)

For a diesel-electric submarine, mission range and endurance depends above all on fuel load. The ratio of fuel carried to fuel consumed improves as a boat gets bigger, so bigger boats have longer range and endurance. So it seems obvious that we can’t buy a boat off the shelf, because no MOTS boat is big enough to offer the range and endurance that our unique circumstances require.

But is that really true? That might depend on whether we’re looking at the capability of each boat, or the capability of the fleet as a whole. Discussions about range and endurance invariably focus on the capabilities of each boat. That’s an understandable preoccupation for those who actually drive them, but it’s not what really matters for the rest of us.

What matters to Australia is the capability of the fleet. As far as range and endurance are concerned, we should be aiming for the fleet of submarines that offers the largest number of days on station in key operational areas per dollar spent. And that depends not just on how long each boat can stay at sea, but on how much it costs.

We can illustrate this general point with a hypothetical example. Boat A is 4,000 tonnes, costs $4 billion and, after allowing for transit to and from, can spend 30 days on station. Boat B, displacing 3,000 tonnes, costs $2 billion, and can spend 20 days on station. In this example, Boat B offers 50% more days on station for each dollar.

Of course we’d need more boats to achieve the same number of days on station, so operational costs would be higher, as would demands for crews. And moving boats in and out of the operational area more often would impose some tactical costs as crews have to familiarise themselves with the specific environment. But a big cost advantage could still lie with a bigger fleet of smaller boats—and it would be a more robust capability in the face of operational losses.

So how closely do the real numbers reflect the hypothetical ones in my example? I don’t know. The sums are more complex than my example suggests, because of possible differences in transit speed, for example. And credible information on the range and endurance of submarines is hard to come by, as is reliable information on costs.

But it’s quite possible that spending $50 billion on a bigger fleet of smaller, cheaper boats would give us more submarines on station, more reliably, and with far lower project and schedule risk than the smaller fleet of more costly and risky big boats that we’re aiming for now.

If advocates of big boats think that isn’t the case, it would be useful to see the numbers on which their conclusions rest. And this question can’t simply be dismissed, as some try to do, by saying that smaller boats simply can’t operate at all at such ranges. The 3,400 ton Collins class boats operate quite successfully a long way from home.

In fact, the more one thinks about it, the more one wonders whether an evolved Collins design would not in fact have been the best option. And the more one wonders whether it isn’t too late to revisit that option…

Unlike nearly all northern hemisphere diesel-electric submarines, the Swedish-designed Collins class is intended to meet a unique operational requirement—to routinely conduct long and distant patrols. This presents many engineering challenges not faced by other navies. To quote a retired submarine engineer, ‘No other navy flogs its diesel-electric submarines thousands of miles across the ocean and then sends them on patrol’.  

Our Oberon class shared some similar characteristics with Collins—including long range. The Oberons travelled on the surface and dived just short of the patrol area, but the Collins was designed to remain dived because of the increasing threat of being discovered at the surface.

The unique operational requirement and the need to remain covert led to many design challenges for Collins. Among these were dealing with the size of the lead-acid main storage battery bank (more than three times larger than the Oberon equivalent) and the large installed diesel-generating capacity (half as much again as the Soryu class). And to ensure peak performance of the battery, the Oberons would conduct a ‘gassing’ charge while still surfaced before reaching the diving position. It takes many hours to gas-charge the battery at reducing rates of power, to get that final 20% of battery capacity.

But the Collins transits in a dived state. In a dived submarine, the engines—which burn the hydrogen from the battery—might have to be stopped for operational ‘events’, emergencies or simply failure to maintain periscope depth. And to prevent an explosive buildup of hydrogen, the diesels must be run for an hour after completion of gassing, so gas-charging whilst dived is not permitted.

Without gassing a lead-acid battery, the cells cannot be charged to full capacity. As explained by Peter Briggs, this means the usable capacity is a much reduced 50% at best. And during a high speed sprint, the capacity is reduced even further at lower states of charge.

To counter reduced performance with cycling and age, maintenance gassing charges are required. These are required several times a year when alongside, and remove at least a week from operational time.

But lead-acid batteries have many good characteristics—reasonable energy density at low patrol speeds, scalability, and sited low in a submarine the mass aids stability. They can be stored dry before commissioning and installation. They are robust to abuse, overcharge and over-temperature operation. After 100 years, the acidic electrolyte and hydrogen are well understood and manageable.

That said, the new high-tech lithium-ion batteries have several advantages. They can store up to 100% greater energy. They can be fully charged quickly, at the maximum charging rate. Even better, lithium-ion retains good performance down to low states of charge. And there is much less maintenance charging and hardly any physical maintenance.

With these advantages, convinced of its safety mitigations, Japan has chosen lithium-ion in its later Soryu class in place of the lead-acid battery and the ultra-quiet Swedish air independent propulsion or AIP. The AIP is effectively like a battery which can extend dived endurance by about two to three weeks, but only at relatively low patrol speeds. Lithium-ion batteries can store around the same energy as AIP but without the complexity, can be used at sprint speeds and can be recharged at sea. So the Japanese approach is understandable.

So why not simply switch from lead-acid to lithium-ion? The French submarine designer DCNS is clear—safety—as reported recently by David Wroe.

Existing commercial lithium-ion cells are complicated. Australia’s Future Submarine would need over 100,000 cells in some 500 modules. For over-charge and over-temperature protection, safety critical electronics is required in each module. In high-energy cells, thermal runaway can occur as low as 120oC and typically releases very high energy, toxic gasses and conductive dust and is almost impossible to extinguish. This requires hardened boundaries between cells and modules with an associated reduction in energy density. Safer chemistries are available, at the expense of energy storage, but they still present significant hazards with release of flammable and toxic materials.

In the life of 100,000 cells and a fleet of 12 submarines there is likely to be a failure that cannot be stopped or controlled, with a catastrophic outcome. The Boeing 787 battery fires and the burning of the US Navy’s Advanced Seal Delivery System are reminders that contemporary lithium-ion is not yet safe enough for submarines.

Although suppliers are beginning to aim for safer chemistries, they require complicated supporting systems, and the value proposition considering safety, cost and performance gains is still questionable. But the advance of lithium is not over. My bet is that the first supplier to select an intrinsically safe lithium ion chemistry and who can still deliver on performance and long life will be the Navy’s supplier of choice.

Transitioning from lead-acid to lithium technology requires a new submarine design. But whether 5 or 15 years away, there is a compelling need to plan for such a transition for Australia’s Future Submarine.