Why might the sinking of a Chinese nuke submarine still worry the US navy?

In late September there was a wave of media articles saying that a recently launched new Chinese submarine sank near its shipyard. Most said it was a nuclear submarine. Now, the whole deal whether there was a submarine sinking or not is not clear even to this day. But what's important is this. If a nuclear submarine did sink, where the articles claim it sank, and if it was a novel nuclear submarine, then that indicates two things. One, China's navy had an accident. But much, much more importantly, it also indicates China finally made a new type of a nuclear submarine that was often rumored but never confirmed. A type of nuclear submarine that might be regarded as a revolution in submarine propulsion. And potentially a serious threat to the future US Navy. All those media articles were plausibly kickstarted by social media write up of an ex US Navy officer, Tom Sugard. This summer he analyzed April and May satellite images of A belated June image showed the convergence of barge cranes at the site where the submarine was once moored, which was interpreted as an indication of a possible accident. Shortly after, media articles started appearing, adding that unnamed US officials suggested that indeed a Chinese submarine sank there. The US officially has not said anything sank. We can't actually know for sure if a Chinese sub sank until we get some images of it being lifted out of the water, or until China says it sank. But considering multiple articles which said US officials told them that, we will assume that it wasn't just an echo chamber, and we will base this video on the proposition a submarine did sink. Now, submarines sometimes sink. A US nuke sub once sank Pearside after it was launched. So a submarine sinking is not that big of a deal. The big deal is that articles said US officials claimed it was a nuclear submarine. China had nuked subs before, so why is that strange? Because it was a novel, compact submarine type with serious implications for the future. The location of the sinking is nowhere near any place that Chinese nuclear subs usually visit. The only shipyard that has to date built nuclear submarines is at Hulidao, far away. The location of the shipyard where a nuclear sub allegedly sank is inland at Wuhan. There's the Wuchang shipyard there, which to date built many conventional submarines. Those are visibly smaller than nuked subs, and those are taken down the Yangtze river to join the navy, once they've been built. But do we know anything about the Yes. There were actual satellite photographs of the submarine taken, before it disappeared. The April one is quite bad resolution, but it was enough to notice the sub was longer than the previous class of conventional subs built at that shipyard. Then CNN came out with this image taken in March. It became very clear we are talking about a completely new class of submarine. What's more interesting, though, is that the sub is still nowhere near as big as China's usual nuclear submarines. When the term nuclear submarine is typically used, what is usually meant is this, a large, ocean-going submarine designed for deployments lasting for half a year, if needed. It can be either an attack submarine, or a so-called boomer sub. A very large sub holding ICBMs with nuclear warheads. Now, nuke attack subs are used to actively track and intercept ships at sea, as they're generally faster than destroyers, carrier groups, and so on. They're hunters. Conventional subs are smaller. Some are very small and coastal vessels, but China generally uses only mid-sized ocean-going conventional subs. Still, even those are slow and have to refuel every few weeks. Basically, their job is to set up ambushes. China's current nuke attack and boomer subs are not as big as their US analogs, but are still quite large. Easily larger than this new sub. Previous Chinese conventional class subs are roughly 5 meters shorter than the new mystery sub. Apparently, the lengthened part is behind the sail, generally where one would insert a new propulsion section. Like, for example, inserting extra batteries, or a nuclear reactor. There have been instances where old subs were cut in half and lengthened by inserting additional sections. In this case, however, the sub has been designed from the start with additional hull sections. The sub is generally of the same width as previous conventional subs, but it appears to have X-shaped tail surfaces, instead of crucifix ones. Two towed array sonar booms may also be installed at the back as well. Otherwise, general design and layout is similar to previous conventional submarines. So one might surmise that the design stems from the similar conventional sub requirements, shipyard limitations, and so on. Has the Wuchang shipyard ever built subs with nuclear reactors so far? No. But so what? There's always a first, of course. That same company used to operate at a downtown Wuhan facility for decades. But as of late 2010s, submarines were built in a new facility in Wuhan's suburbs. Who's to say that one of the added capabilities of the new complex is not work with nuclear reactors? Unnamed US officials from the articles also said they don't know if the nuclear sub contained nuclear fuel or not. Which is to say, it's theoretically possible that a ready-made reactor was installed in the submarine, but nuclear fuel itself was not in the reactor, perhaps to be inserted at a completely different facility, perhaps one having more experience with that. Large attack subs have big reactors with lots of fuel to last them for decades. But if speed requirements are modest, if the sub is smaller, then a small reactor might suffice. And even less fuel might be needed if the reactor is made to be refueled more often, through a special hatch. Refueling big nuke subs required cutting the hull, precisely because it was almost never needed. Now, we don't know if indeed that Chinese sub is meant to be refueled often. But we do know that it's around half the displacement of a typical nuclear attack sub. Now, imagine that the mission requirement is not to provide bursts of speed going 30 knots or more. Instead, the reactor might be there to feed the power plant a constant low steam supply. Enough for, say, 5 or 10 knots. Faster is always better as long as it doesn't add too much noise. But 5 to 10 knots indefinitely is still way better than 5 to 10 knots for, like, 1 to 2 weeks. The power requirement doesn't rise linearly with displacement. This paper on air independent propulsion for submarines suggests that a 3000 ton sub going at 5 knots is using approximately 100 kilowatts. At 10 knots, it uses some 550 kilowatts. Our figures adjust for the constant power load to run life support and electronics, which is usually 100 to 200 kilowatts at all times. But at high speeds, extra power load really shows. At 20 knots, it is now at 4500 kilowatts. Or over 40 times more for propulsion, even though the speed was increased by 4 times. That's why nuke attack subs have huge propulsion sections. The stuff about small reactors is not purely hypothetical. There has been research undertaken about possible benefits of small nuke reactors, for such small power loads, on submarines. For decades such research would appear in the west, but nothing came of that. By the end of the cold war, the US got rid of their small conventional subs altogether. And most other users did not have the money or the need to pursue such small reactors. Especially after the end of the cold war. The soviets did experiment with one such sub. In the mid 1980s, they put the somewhat compact reactor, by their standards, inside an old conventional submarine. But as the soviet union fell apart, such experiments were not repeated. Today, the Chinese navy is all that the soviet navy was, and then some. It has more money, more resources and access to better technology. It's no wonder it would be trying out such new technologies. In 2017, a retired PLA navy admiral held a lecture at China's Northwestern Polytechnical University, and, among other details, said that China may be working on low-power auxiliary nuclear power plants that can be fitted on conventional submarine designs. There have been occasional rumors on construction of such submarines since. One set of rumors said components for the first batch of four low-power nuke subs are to arrive at the end of 2024. That sort of makes it initially unlikely that the photographed sub was nuclear. Unless it was an experimental vessel, to test out the concept before the first batch was assembled. Which does make sense. What does all that mean operationally for China and the US? China would get a new class of submarines which would share some traits with both conventional subs and nuclear subs. The new subs would get basically unlimited underwater endurance. Limited only by food supplies, maintenance needs and so on. Larger nuke attack subs can even do six month deployments. These new smaller nuke subs would likely deploy for shorter stints, but even at two or three months, it would still be a big change from today's endurance of conventional subs. As those months could be spent completely underwater. Not like today, where an AIP submarine can spend maybe two or three weeks underwater in total, before having to go back someplace to restock on fuel for its AIP system. Speed-wise, the new sub would be similar to conventional subs, and not nuke attack subs. Everything from the reactor to the air-independent Stirling engine would be sized up to a constant fairly low power output. It might be 5 to 6 knots like in a regular conventional sub. Or even 10 knots. That's impossible to say right now. Additional short bursts of speed powered by batteries would help increase those figures. Today, most of China's conventional submarines basically trawl along slowly at 5 or so knots. They protect Chinese shores. But whatever they do, they either have to go back to base in a few weeks, or they have to be restocked someplace safe while surfacing for hours. That too involves transit time which is lost, or time in base before another deployment. Basically, there are fewer subs on station where needed. With the low power nuke subs, a bigger percentage of subs would be on station where they are needed, potentially achieving somewhat higher cruise speeds. Even a 5 to 10 knot difference for a cruising sub can be a lot. And can mean a difference between reaching the Philippines from, say, Hong Kong in less than 2 days, compared to 3 and a half days for a conventional sub. A 5 knot extra speed dash could also help the sub react better to a new situation, positioning itself in time. Such novel subs would basically spend less time near the surface. Being underwater is of the utmost importance for a submarine, as then it can't be detected so easily by now ubiquitous aircraft and their radars. But how would the propulsion work on such small nuke reactor subs? And how does it compare to other Chinese subs? Today, China's conventional subs have a diesel engine, which is turned off during dives, as it needs fresh air. They also have an air-independent Stirling engine. Its working fluid is then heated by an outside source, like by oxygen and diesel fuel burned in a pressurized combustion chamber. Produced heat drives the Stirling engine, which then drives the propeller shaft and a generator, which fills up batteries as needed, for when more power is suddenly needed. Stirling engine itself is best when kept at continuous power levels. Cruise speed of air-independent propulsion subs are usually estimated at 4 to 6 knots. Typical nuclear attack sub has its nuclear reactor providing steam to the steam turbine, which then turns the propeller and powers the electrical generator. Steam turbines can quickly ramp up power for speed dashes. Nuke attack subs can often rely on dashes in their missions. But conventional subs are largely about ambushes. So a constant power from a Stirling engine may be enough. And what little extra power burst may be needed at times could come from stored electricity in batteries. That's basically how conventional AIP subs work today as well. Using AIP for cruise and batteries for short power bursts. This new low power nuke could go a few ways design wise. But a setup rumored some years ago does make sense. Instead of the diesel engine, a small nuclear reactor is inserted. It provides steam and that steam heats the process in the Stirling engine. So a separate combustion chamber, oxygen and diesel tanks are not needed. There is no exhaust. The Stirling engine can then either turn the propeller more directly, or it can power an electrical generator. The latter is more likely for a modern submarine, as such a layout is what new submarines seem to be going for. US Columbia class nuclear sub will use an electric drive. Also, a Stirling engine might produce a bit less noise than a comparable steam turbine. It's a closed cycle process, steam pressure is lower, and there are fewer moving parts in it. Low noise is one of the important features for a submarine. Pure battery operated subs are quietest. But even with modern lithium ion batteries, we're probably talking about 10 or so days of endurance for a modern sub like the Japanese Taigei class. Old lead acid batteries are roughly 3 to 4 times less power efficient than the proven lithium ion models. Hydrogen fuel cell based AIP is the second most quiet solution, and Germany uses it a lot for its smaller coastal submarines. Stirling has moving parts, so it makes a bit more noise than fuel cells, but it's a decent choice for larger submarines. Now, a nuclear reactor in itself is quiet. Today's submarine reactors don't even have to use coolant pumps, but rely on natural circulation, even for high power speed dashes. A low power reactor in this new Chinese sub would need no pumps. The rest of the machinery is fairly quiet, certainly not louder than the current Chinese Stirling engine subs. And if pure electrical drive is used, which doesn't need a gearbox, then the overall noise levels can drop even a bit more, compared to today's Chinese subs. Nuclear reactors have the additional benefit of having enough power to extract oxygen from the water through electrolysis. Conventional subs might find said process too power demanding in the long run, either cutting into their battery capacity or simply limiting their dive time. How might the Chinese fleet look with those new subs in the near future? Today, China operates little over 45 conventional submarines. Over half of that number are older types that don't have air independent propulsion. Those might be the first to be replaced with the small nuke reactor subs. China was building anywhere from 2 to 4 conventional subs per year, not counting production levels when it would be switching to a newer model. It seems less likely that the higher end figure would be achieved in the near future, given the cost. But 2 or so per year would be perfectly doable for a shipyard like the one near Wuhan. Nuclear reactors are costly, but again the overall sub is smaller and less capable than a big nuke attack sub. So its plausible cost would be somewhere in between the nuke attack and a conventional sub. Adjusted for Chinese salaries, of course. Plus the smaller sub would have a smaller crew, resulting in smaller annual costs. Submariner salaries aren't cheap, costing over 150 thousand dollars annually, each. The difference for two crew sets over 30 years of lifetime of one submarine can be like 0.7 billion dollars. Again, the small 4 nuke sub would likely have a few more crew members than a pure conventional sub. Overall, the new sub class might result in China increasing the number of its nuclear subs, without breaking the bank. Sure, some of those will be the smaller, less capable nuke subs, but it would still be a massive step up in capability than using a conventional sub fleet. It's not that the underlying technology is something new. It's just that until now, no other navy had the right combination of geographical prerequisites, mission requirements and money to make such small nuke subs viable. For a navy with a huge budget like China's, investing in these kind of sorta nuke subs could be worthwhile. For somewhat less money, they get something that's quite tailor made for defensive coastal operations. And for the missions requiring long range hunts, true nuke attack subs are used. Production of which China has also been ramping up. So China may be aiming to have a mix of smaller, slower and larger, faster nuke subs. Not quite following the US mantra of large, fast nuke subs only. And not quite following the soviet mantra of a mix of nuclear and conventional subs. Naturally, the switch would not come overnight. There are still a few decades of life in current modern conventional subs, so it might be the 2050s until we see the last Chinese conventional sub retired. With half of the denier force composed of larger nuke subs and half of these more compact nuke subs. By 2040, some conventional subs should still be in service. So the whole sinking of Chinese submarine isn't a real interesting deal here. If a submarine did sink, it was a claim it was a nuclear sub that's interesting. As it points to very novel developments in nuke sub technology, future Chinese fleet composition, ability of Chinese sub fleet and the overall future balance of power in the pacific.