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Recently Australia decided to acquire nuclear-powered submarines, attracting several negative comments, such as:

Malaysia said on Saturday that Canberra's decision to build atomic-powered submarines could trigger a regional nuclear arms race, echoing concerns already raised by Beijing.

"It will provoke other powers to also act more aggressively in the region, especially in the South China Sea," the Malaysian prime minister's office said, without mentioning China.

Source

And

WELLINGTON, Sept 16 (Reuters) - New Zealand Prime Minister Jacinda Ardern said on Thursday that Australia's new nuclear-powered submarines would not be allowed in its territorial waters under a long standing nuclear free policy.

Source

And

SEOUL, Sept 20 (Reuters) - North Korea warned on Monday that the United States risked a dangerous nuclear arms race by providing submarine technology to Australia, criticising its "double standards" and vowing counter-measures.

Source

How are these objections explained? As I understand nuclear submarines, they are simply ordinary submarines with a superior energy source that lets them operate at high speeds for long periods of time, and frees them from having to refuel and/or to surface. Adopting nuclear submarines then sounds like adopting cars instead of horse-drawn carriages - it's just the sensible thing to do.

From this perspective Malaysia's and North Korea's objections don't make sense since it's not like the submarines are nuclear-armed, so I don't see how they would trigger a nuclear arms race. New Zealand's "nuclear free" policy also doesn't make sense, since they are presumably allowing PET scanners into the country and those rely on nuclear physics too.

What am I missing?

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    It should be noted that nuclear powered subs != nuclear weapons. They are just used for better performance at sea. Longer times underway and underwater without refueling.
    – Joe W
    Sep 20 at 1:12
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    @JoeW that's exactly what I'm asking - why would anyone not get nuclear powered submarines if they have better performance? But if that's the case, why would anyone react negatively to Australia acquiring them?
    – Allure
    Sep 20 at 1:21
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    @Allure NZ is just reiterating its long-standing stance regarding nuclear powered vessels - Australia cannot send its nuclear-power submarines through NZ waters, which means that Australia has to go around those waters. NZ isn't jealous, it specifically does not want the capability and it does not want those with the capability to send nuclear powered or armed vessels into its waters. This has caused significant issues for NZ in the past, with the US throwing its toys out of the pram and effectively putting sanctions on NZ in the 1980s - and yet the ban survives to this day.
    – user16741
    Sep 20 at 2:33
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    @jamesqf thats six of one, half a dozen of another really. Its not as if China is completely on its own in terms of being provocative in the region...
    – user16741
    Sep 20 at 4:27
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    New Zealand's nuclear-free legislation specifically forbids the use of nuclear power for military purposes (be it weaponry or propulsion) within New Zealand's territory. It's not a ban on the understanding or use of nuclear physics
    – llama
    Sep 20 at 15:49
51

There are two aspects to this - nuclear powered submarines can stay on station for essentially an indefinite period of time, which means that your nuclear-weapon-armed ballistic missile carrying submarines have a greater chance of being "lost" by your opposition's attack boats.

But this benefit also applies to your opposition's attack submarines - if they are nuclear powered (not nuclear armed, they are there to destroy your nuclear-armed submarines, which they will do using conventional high explosive weapons), they can stay on patrol longer tracking your submarines...

The more attack submarines your opposition has, the more likely your offensive submarines (nuclear ballistic subs) are tracked for their entire patrol, and will be taken out the moment you need them in a shooting war.

So, the only way to counter this, and ensure that you have enough ballistic weapons ready to launch, is to do two things:

  1. make sure your submarines are as stealthy as possible - which means nuclear power

  2. make sure you have enough submarines so that some of them slip through your opponent's nets - if you have more offensive submarines than they have attack submarines at sea at any point in time, then you win the math

So there is the nuclear arms race - together, currently, the UK and US have X number of nuclear attack boats to dedicate against the Chinese ballistic submarine fleet. Add more boats to that by bringing an Australian fleet into the mix and China will counter by increasing the number of ballistic submarines in its fleet - which means more nuclear weapons.

In the "good old days", you would have heard this referred to as a "submarine gap", in the same vein as "missile gap", "bomber gap", "fighter gap" - lots of noise about these things during the Cold War, which roused politicians into spending more money on more submarines/missiles/bombers/fighters/whatever in order to ensure that they were not out-gunned by the opposition.

New Zealand's "nuclear free" policy also doesn't make sense, since they are presumably allowing PET scanners into the country and those rely on nuclear physics too.

That's a reductio ad absurdum argument, because New Zealand's legislation in this area prevents nuclear powered vessels and nuclear weapons to enter its territorial limits - it does not limit nuclear power stations within NZ, nor medical or scientific instruments.

So, PET scanners et al. are perfectly fine, as are NZ-based nuclear power plants should the government decide to build them.

1
  • Comments are not for extended discussion; this conversation about nuclear deterrent has been moved to chat.
    – Philipp
    Sep 24 at 8:44
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US nuclear-powered submarines use highly-enriched uranium (HEU) as their power source. (The UK ones also use HEU, sourced from the US, but processed locally into cores.) So, critics say/claim HEU-powered submarines are similar enough to a floating dirty bomb, which they don't want entering their waters. See for example this complaint/claim from a NZ group.

“If we allowed any nuclear submarine into Auckland or Wellington Harbours a nuclear accident resulting from collision, grounding, fire, explosion or reactor leaks could have dire consequences for human and marine life and jeopardise shipping, fishing, recreation and other marine based activities for generations.”

“Another concern is that the nuclear reactors in the submarines to be acquired by Australia use highly enriched uranium (HEU) rather than low-enriched uranium (LEU) - the normal fuel for nuclear reactors. HEU is the principal material required to make a nuclear bomb. [...]

And even some Australian groups opposing the deal say something similar, albeit in terms of risk of pre-emptive attack, besides accidents:

The Nobel Peace Prize-winning International Campaign to Abolish Nuclear Weapons (ICAN), Australia tweeted about the deal: “The nuclear-powered submarine deal raises serious concerns over nuclear proliferation as the UK and US’ models use highly enriched uranium.

“This is not prestige, this is provocation.”

“Important questions remain over construction of the submarines and the potential imposition of military nuclear reactors on Adelaide or other cities, making construction sites and host ports certain nuclear targets,” said Gem Romuld, Director of ICAN Australia.

“Military nuclear reactors in Australia would present a clear nuclear weapons proliferation risk and become potential sites for nuclear accidents and radiological contamination long into the future.”

Green Party leader Adam Bandt even likened the move to putting “floating Chernobyls in the heart of Australia’s cities”.

He said it makes “Australia less safe”.

NZ has maintained a long-term policy of not allowing nuclear-powered vessels (HEU or otherwise) from entering its waters:

"New Zealand's position in relation to the prohibition of nuclear-powered vessels in our waters remains unchanged," Ardern said.

The ban was introduced in the wake of French nuclear testing in the Pacific and led to the US navy banning its warships from entering New Zealand ports for more than 30 years.

The destroyer USS Sampson visited in late 2016 but only after the then-prime minister John Key gave a special exemption, saying he was "100 percent confident" the vessel was not nuclear powered or carrying nuclear weapons.

(Based on DVs) you may think this is bollocks and nonsense, but the uniform treatment of the nuclear-powered and nuclear-armed vessels has been a long standing policy of the Labour party in NZ, since back in 1985.

[PM David] Lange sought to soften Labour Party policy on this issue but found little room to move; party activists were unwilling to draw distinctions between nuclear propulsion and nuclear weapons.

I'm not sure if the Labour party itself has articulated the 'why' angle on nuclear-powered in anymore detail, so I gave you some NZ NGO's take further above, why they fear/oppose HEU-powered in particular.

Interestingly though, concerns about naval reactor designs were voiced (by NZ) back in the 1970s as well:

concerns about the safety of nuclear-powered ships first emerged on the political agenda. In 1972, Labour Prime Minister Norman Kirk declined the application of an American nuclear-powered submarine to visit New Zealand based on safety concerns. New Zealand had requested technical details of the reactor which the United States had refused to give. Moreover, neither the United States nor the United Kingdom were willing to pay compensation to New Zealand if one of their visiting ships had an accident in port. Thus, this was not a move to prohibit nuclear-powered ship visits. Kirk was only pushing for a declaration of full liability to be paid by the American or British government in case of accident. In fact, a number of other countries including Australia had imposed similar restrictions on nuclear-powered ship visits on the same grounds. In 1974, the U.S. gave New Zealand ‘an absolute guarantee of liability for any nuclear reactor accident’ and the United Kingdom followed suit in 1976. Although visits by nuclear-propelled warships did not take place between 1971 and 1976, conventionally-powered ship visits still occurred. The National Government under Robert Muldoon allowed for the resumption of visits by nuclear-propelled vessels in 1976.

As visits increased under Muldoon (and based on declassified cables, mostly due to his government's requests than any needs of the US) there was political backlash... but this initially did not have nuclear-power in its sights, although that came about in 1983

Richard Prebble’s first attempt to introduce an antinuclear legislation into Parliament. In 1976, he called ‘for the recognition of the South Pacific nuclear-free zone.’ After failing to get a majority in Parliament, Prebble made a second attempt in 1982, this time with the Nuclear Free Zone (New Zealand) Bill. He pointed out that ‘his bill would not ban visits of nuclear-powered ships ... It dealt solely with whether parliamentarians were prepared to allow nuclear weapons to be brought into New Zealand.’ This bill was equally unsuccessful. One year later, on 3 August 1983, Bruce Beetham, leader of the Social Credit League, attempted to introduce the Prohibition of Nuclear Vessels and Weapons Bill. As Beetham stated,

although expensive to build, nuclear powered ships do not need constant refueling, and for that reason they are ideal vehicles for the offensive role that falls to the Navy. That being so, such vessels will almost invariably—in fact, one could almost say automatically—be armed with offensive weapons, which must include nuclear weapons.

Thus, Beetham’s bill was the first attempt to introduce a ban on nuclear-powered ships to parliament because such ships were almost certainly armed with nuclear weapons. In the end, the bill was defeated by 40 to 39 votes.

The following year, Richard Prebble launched his third attempt to make New Zealand nuclear-free. On 12 June 1984, Prebble introduced the Nuclear Free New Zealand Bill. This time, also Prebble’s bill called for the exclusion of nuclear-powered ships from New Zealand. As Prebble explained, the bill ‘prohibits the entry of nuclear powered ships and nuclear weapons into New Zealand and further prohibits the building of nuclear reactors within New Zealand.’ Prebble almost succeeded to introduce this bill because National Party MP Marilyn Waring threatened Prime Minister Muldoon to cross the floor and vote for Prebble’s bill against her own party caucus. As a result, National Party MPs prevented Waring from speaking in Parliament that day by raising numerous points of order until Waring’s time to speak had expired. On the following day, Prebble’s bill was defeated by 40 to 39 votes just like Beetham’s bill one year earlier. Nevertheless, Waring did vote for the bill together with her colleague Mike Minogue. Prebble’s bill was only defeated because two alienated Labour MPs had voted with the government.

So NZ really came just one vote short of banning nuclear reactors on its soil as well, during that era. (After a snap election, which saw Lange become PM, the Bill amended again to not mention soil-based reactors anymore, passed 42 to 30.)

From the same source, the NZ right wing (such as the ACT party) contends however that the ban on nuclear propulsion made/makes no sense and it's simply a convenient cover for anti-American sentiments within the left. Some Labour MPs that in the meantime have defected to ACT but were privy to the discussions within Labour at the time (such as Ken Shirley) assert this.

After the Cold War ended and the US declared in 1992 that its surface ship won't carry nuclear weapons on port visits, under PM Jim Bolger (of the National party), NZ ordered a review of the law section (11) of the Bill that bans nuclear propulsion in particular. The [Somers] commission appointed for this was attacked in the left-wing press even as its proceedings were underway, since some of its members were well-known supporters of admitting nuclear-powered ships. So its (predictable) final report didn't really change any minds and Bolger gave up on the idea of changing the law, apparently without putting it to a vote. Some have even commented (there are ample quotes in that thesis) that given the political capital invested by New Zealanders in confrontation with Washington, the ban (on nuclear propulsion) had acquired symbolic importance, and giving it up meant tarnishing New Zealand's image as nuclear-free and was seen as a capitulation to US demands. Others opponents insisted on the safety angle, contending that it wasn't good enough.

There was apparently another attempt in 2005 by the ACT party to have the ban on propulsion rescinded (which isn't covered in that thesis), apparently also without success. According to Wikipedia

John Key promised in 2006, just after being elected leader of the National Party, that "the nuclear-free legislation will remain intact" for as long as he is the leader of the National Party.

Keys was PM from 2008 to 2016.


The Malaysian objection doesn't seem incredibly specific, other than pointing to an arms race. Perhaps vying to be a regional power, Malaysia feels like it would be forced to increase its own navy spending to keep up with the improved Australian one and likely Chinese response. As Reuters commented:

"It will provoke other powers to also act more aggressively in the region, especially in the South China Sea," Malaysia's Prime Minister Office said in a statement.

The statement did not mention China, but Beijing's foreign policy in the region has been increasingly assertive, particularly its maritime claims in the resource-rich South China Sea, some of which conflict with Malaysia's own claims.

Malaysia only has two submarines (and they plan to have 4 ... by 2050); that's fewer than even its much smaller neighbor, Singapore. So Malaysia probably doesn't feel too good about others in the region getting even farther ahead of them, in this department.

They also reference ZOPFAN, which seems to be some kind of non-aligned movement treaty, so perhaps Malaysia is also resenting more involvement of the Western powers, but I'm not too sure about that. Actually, digging up more material on ZOPFAN, that seems to be the case:

ZOPFAN, the Zone of Peace, Freedom and Neutrality in Southeast Asia, was another Malaysian initiative, advanced at a time when Britain had withdrawn the bulk of its forces from the region and the United States had begun to come to terms with the People's Republic of China. The archives in Wellington, like those in London, help to document the concept. Tun Ismail, former Minister of Home Affairs and advocate of regional association, had in fact presented the idea in a debate on defence in the Dewan Rakyat back in January 1968, his aim being to save money that could be spent on social services. “The time is … ripe for the countries in the region to declare collectively the neutralization of South-East Asia. To be effective, the neutralization … must be guaranteed by the big powers, including Communist China … it is time that the countries in South-East Asia signed non-aggression treaties with each other. [...]

In a speech in July 1971 Prime Minister Razak argued that the involvement of major powers was the essential reason Southeast Asia had not been at peace for twenty years. Peace and security could be safeguarded only by “a policy of neutralisation which will ensure that this region will no longer be a theatre of conflict for the competing interests of the major powers”.

It should also be said here that other ZOPFAN signatories like Singapore actually welcomed the AUKUS announcement.

Others (e.g. the NZ peace group I quoted from previously) have more explicitly raised the possibility that Australia or its neighbors might be a step closer to nuclear weapons this way:

“Although Australia is not interested in using HEU to make a nuclear bomb, providing Australia, a state member of the Nuclear Non-Proliferation Treaty (NPT), with HEU (at around the 50% enrichment level) for nuclear-powered submarines, could open the floodgates to other countries acquiring HEU powered submarines in order to develop a capacity to then make a bomb. [...]

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  • 2
    British nuclear submarines use a reactor design entirely of British origin - we share warhead design, manufacture and maintenance with the US however.
    – user16741
    Sep 20 at 8:22
  • 2
    @Moo: they use HEU though, provided by the US according to this source. "Currently, US and UK naval reactors are fueled by weapon-grade highly-enriched uranium (HEU) containing 93.5% of the chain-reacting isotope, U-235. (UK reactors are based on US designs and fueled with US HEU.)"
    – Fizz
    Sep 20 at 8:23
  • 2
    Yes, we share (and buy) fuel, doesnt mean we share technology - we have our own manufacturing and processing facilities, and the reactors are entirely UK designs.
    – user16741
    Sep 20 at 8:40
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    "HEU-powered submarines are similar enough to a floating nuclear bomb..." This is misleading and does not appear in the link cited. The geometry of these reactors means it is not possible to explode like an atomic bomb, despite being constructed with highly enriched uranium (HEU). They can experience accidents which could release radioactive material, one of the concerns addressed in your link.
    – chadnt
    Sep 20 at 15:01
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    @Fizz “by how the technology got into British hands in the first place” - by that you mean, we gave the US all our info and scientists at the start of WW2, advanced US understanding drastically, thus allowed the Manhatten project to have years cut off its timescale, but then got screwed by the US at the end of WW2 when they classified everything and shut British scientists out? British scientists literally couldnt read papers they wrote the day before. Dont make out that the US gave poor old Britain the tech and we couldnt develop anything ourselves.
    – user16741
    Sep 20 at 19:36
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Because the use of nuclear reactors on warships blows a giant hole in the Non Proliferation Treaty (NPT):

There is already a military reactor loophole in the NPT. Article III.1 provides that: Each non-nuclear weapon state party to the Treaty undertakes to accept safeguards, as set forth in an agreement to be negotiated and con- cluded with the International Atomic Energy Agency…for the exclusive purpose of verifi- cation of the fulfillment of its obligations as- sumed under this Treaty with a view to preventing diversion…from peaceful uses to nuclear weapons or other explosive devices. By omission, the NPT therefore allows withdrawal of fissile material from international safeguards for use in military reactor fuel.

enter image description here

Source: https://fissilematerials.org/library/ma01.pdf

This is especially true for submarines, where due to extreme compactness requirements and difficulty of refueling once installed, very highly enriched (93% for US submarines, source: same doc.) Uranium is used, to allow a small reactor to operate for years without refueling. This is the tech that would be shared with Australia, since that's what US submarine builders know.

Iran has been in no end of trouble for enriching ~200kg of Uranium to 80%. What if they could say "BTW, we're enriching 20000kg of Uranium to 93% for our new nuclear submarines; if Australia (and Brazil, Korea, Japan, Italy, etc at that point) can do it, so can we!"?

It's for this reason that the US has been fighting tooth and nail to prevent the spread of nuclear propulsion beyond the NPT powers for 5 decades now, only to turn on a dime in the interests of their anti-China alliance.

P.S. In some amazing chutzpah, the official Australian line is that the contract was cancelled because the conventionally powered French design wasn't capable enough and they need a nuclear one, while it is a conversion to diesel-electric propulsion (at great French cost) of the nuclear powered Barracuda class submarine, precisely because everyone thought that a nuclear sub was off the menu.

SYDNEY — Australia’s prime minister, Scott Morrison, said Sunday that it had “deep and grave” concerns about the diesel-powered submarines it planned to buy from France — and that Paris knew that well before Canberra abruptly canceled the deal in favor of sharing nuclear submarine technology with the United States and Britain.

Morrison was pushing back on criticism from France that Australia left the country in the lurch by secretly negotiating the new three-nation pact, called AUKUS, even as he acknowledged telling France about the new deal only on the day it was announced.

“I think they would have had every reason to know that we had deep and grave concerns that the capability being delivered by the Attack Class submarine was not going to meet our strategic interests,” Morrison told reporters Sunday.

-- https://www.washingtonpost.com/world/2021/09/19/submarines-france-australia-concerns/

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    @Eugene That quote just says that they had "deep and grave concerns" about whether the French-designed ships would "meet [their] strategic interests." It doesn't say anything specifically about that concern being related to diesel vs. nuclear propulsion. It could be delivery date, speed, range, cost, etc. (or some combination of all of the above.)
    – reirab
    Sep 20 at 21:32
  • 1
    @reiarb has elaborated quite nicely. We don't know the full reasons why Australia has changed its submarine acquisition plans, beyond what has been stated. What you claim the PM stated is incorrect. To then double down and assert the PM is lying based on this mischaracterization of his statements is clearly wrong.
    – NPSF3000
    Sep 20 at 21:51
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    @reirab "deep and grave concerns that the<<capability>> being delivered by the Attack Class submarine was not going to meet our strategic interests" obviously speed, range and all other capabilities of diesel subs are inferior to nuclear subs by their nature. What makes this so utterly disingenuous is that the French converted their state of the art nuclear sub design to diesel-electric to satisfy the Australian requirement only to be told (on 1h notice!!!) that their diesel sub is inferior and the contract is cancelled without a chance to submit a bid with the original nuclear sub.
    – Eugene
    Sep 20 at 21:53
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    @NPSF3000 The full reasons are pretty obvious: Australia has signed onto a new anti-China alliance and France hasn't. I was merely pointing out the lameness of the official excuse, not suggesting that it has any relation to the real reason in any way shape or form.
    – Eugene
    Sep 20 at 22:01
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    @NPSF3000 Again, the prime minister specifically mentioned the deficient <capabilities> of the (diesel) subs. He cancelled the contract without giving the French a chance to bid on a nuclear sub contract(that would have been easier for them in the first place) that could have those capabilities and simultaneously announced a new (no bid) contract from members of a new military alliance. This is 100% political and the excuse is lame and transparent.
    – Eugene
    Sep 20 at 22:28
9

There is a major difference between a nuclear powered submarine and a PET scanner. New Zealand doesn't ban PET scanner but they do ban nuclear power plants and that is what powers a nuclear submarine. A sufficiently bad malfunction of a nuclear power plant can lead to a Chernobyl kind of event. A PET scanner cannot. One can of course discuss how high the risk is but that is besides the point. New Zealand decided that they do not want to have nuclear power plants (and much less nuclear weapons) on their territory. Therefore they ban any nuclear submarines from their territorial waters.

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    FYI, the standard English spelling is Chernobyl; that Tchernobyl spelling seems to be used in French. Obviously both are transliterations of a Cyrillic name, and some like czar vs. tsar have multiple well-known transliterations / spellings, so the Tchernobyl spelling is comprehensible to native English speakers (at least it was to me), especially given the context. Sep 20 at 15:51
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    The ban is on use of nuclear power for military purposes, as @user253751 said civilian nuclear power plants are not banned (there's just no use for them since hydro power is so abundant)
    – llama
    Sep 20 at 15:53
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    While a nuclear powered sub having a catastrophic malfunction would be bad news for the crew of the sub, and possibly some nearby marine life, it would be nowhere near a Chernobyl-level disaster, which rendered a large area uninhabitable for decades. Sep 20 at 17:06
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    Well, we're also talking about a much smaller reactor. As far as Chernobyl is concerned, large parts of the initially affected region are now, only a few decades later considered relatively safe, I wouldn't be surprised to see much of it mostly resettled in 50 years or so (except for immediately around the power plant - that could indeed be millennia). Still a far greater impact than one sub would have of course. Sep 20 at 18:06
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    note: New Zealand actually HAS a nuclear reactor (for research purposes) gns.cri.nz/Home/Our-Science/Nuclear-and-Isotope-Science
    – Isaac
    Sep 21 at 4:57
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From the point of view of other countries located between Australia and China, IMO the issue is not specifically with the power source or performance of the submarines, although if you faced the risk of another country's attack sub sunk in your local waters, you would probably wish it were not nuclear powered.

But more so, the larger issue is that the focal point force buildup in the US-China conflict is shifting to Australia, as opposed to, say, Okinawa. So the geographic line along which any potential battles are to take place passes through the countries of Southeast Asia, in particular Indonesia, Malaysia, and also, Thailand, Laos and Cambodia (from the point of view of Chinese air defense against IRBM's that may eventually be stationed in Australia (recently discussed along with the cooperation on subs).

As luck would have it, there is a relevant history of great power proxy conflict in the post-cold-war period to draw from in the region. Outcomes for the geographically adjacent countries were, on the whole, not good.

Additional reading:

On concerns about shifting the focal point of militarization and potential conflict to SE Asia -- Why is Southeast Asia so concerned about A-UK-US Plans for nuclear submarines [The Conversation; also published at SCMP but paywalled there]

On future US base expansion in Australia -- US seeking basing in Australia after Submarine Deal [Foreign Policy]

1
  • @Martin Schröder -- added some links
    – Pete W
    Sep 20 at 21:24
3

There is a realistic fear that China could use Australia's deployment of a nuclear submarine force so far from Australia's shores as a justification to push its own capabilities further.

Because of historic reasons the Chinese people see themselves as being the victims of foreign aggression, rather being an aggressive people themselves.

As a direct consequence, Beijing tends to only deploy military forces in a configuration that it can sell to its people as being defensive. For example, placing anti-aircraft batteries on disputes islands, rather than ballistic missiles. Because form a psychological perspective an anti-aircraft battery is a defensive weapon, rather than an offensive one, because the enemy has to come to you rather than the other way around. Even the placement of weapons adjacent to Taiwan is justified in this way.

If Australia is seen moving nuclear submarines towards China, Beijing can justify pushing its own military out in that direction in order to counter Australian forces without breaking the psychological hold that China's victim ideology has on it.

TLDR: This could start an arms race.

5
  • How would this be different if Australia's subs were powered by diesel instead of nuclear reactors? Remember that "nuclear submarine" here is referring to the fuel source for the submarine's propulsion. It is not a reference to carrying nuclear weapons, which these submarines will not be doing. Contrary to what the name might suggest, an "attack submarine" - regardless of its propulsion source - is primarily intended these days as a defensive weapon against submarines armed with nuclear weapons. That is, it's designed to destroy said subs before they can launch nuclear missiles.
    – reirab
    Sep 20 at 21:28
  • 2
    @reirab see my answer to cover that - basically, the more decent attack subs there are fielded against you, the more SSBNs you need to ensure your capability is unhindered when its needed. Nuclear-powered attack subs can stay on station and patrol longer than diesel-electric ones, which means that SSBNs can be covered for their entire patrol period rather than just parts of it.
    – user16741
    Sep 21 at 0:41
  • 2
    @Moo Yeah, I read your answer and it's good, but answers should stand on their own. Currently, this one doesn't explain anything about why the effect described in the answer would be any different with nuclear-powered subs vs. diesel-powered ones.
    – reirab
    Sep 21 at 2:15
  • We've been in an arms race, look at the building of hypersonic missiles and the INF treaty being torn to shreds. Sep 22 at 15:13
  • In the context of China it's about psychology. China believes itself to be the victim of foreign aggression so it organizes its military in a defensive configuration that sticks close to home. Mentally, China can't justify possessing a force capable of engaging Australia because it's too far away to be a threat. Long range forces would be offensive, not defensive. Thus mentally off limits). But If Australia were to poses long range subs then China would feel justified in possessing long range capabilities to defend against them. Once you understand the Chinese mindset it's obvious.
    – user38958
    Sep 22 at 19:31
3

Technically speaking, a contemporary diesel-electric submarine is extremely quiet when submerged.

However, and this is critical: a modern nuclear sub, especially one out of a US shipyard (that build the quietest nuclear subs), has a much greater range that it can travel undetected, and a much greater array of options in an actual conflict.

A diesel-electric sub can travel at a quiet 10 knots for a few hundred nautical miles at most, after which it must recharge its batteries and refresh its internal air supply for the crew, where it will make a fair amount of noise that can be detected.

The diesel electric sub must also plan its moves to have enough battery charge to escape during an actual conflict, limiting its effective range even more. And finally, in the event of conflict, the diesel electric sub can't travel at high speed to escape an attacker for very long before its batteries are exhausted.

For that reason, diesel-electric submarines are considered defensive, as they can't transit great distances without being detected, and have a fairly short range in combat conditions. Best suited to defending one's coast lines, where local air and naval assets can also be brought to bear.

The nuclear submarine, limited only by the food on board for the crew, has a submerged endurance of months, and can travel at a quiet 10 knots for those months, not a few hundred nautical miles. It can transit anywhere on Earth and remain undetected. The first time a potential adversary will know about the presence of a nuclear sub is when ships start exploding. And it has full power to maneuver or escape, at any time. It can run at its top speed for weeks, which is as fast or faster than almost all surface ships. Nukes do their damage, and then they disappear, maybe to reappear hundreds of miles away.

Due to these capabilities, the nuclear submarine is considered a strategic offensive weapon that can carry the conflict to an opponent's shoreline, and a very powerful weapon at that.

So, Australia getting nuclear submarines gives it a global strike capability that they didn't have before. With their current aging Collins class subs, they couldn't effectively operate at any great distance from their coast without being detected, and anti-submarine efforts could find them fairly quickly.

In a potential Asian conflict, that gives Australia the ability to attack the vital shipping lanes that China depends on to keep its economy operating, both for exports and oil imports, that Australia couldn't do with diesel electric submarines. That is probably China's greatest vulnerability in a conflict, having its economy implode due to a cutoff of shipping... which is also a likely reason they have been rather pushy around those shipping lanes.

Given the recent diplomatic row between the two nations, this move complicates the implications of a regional war considerably.

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