Why is the Virginia as small as it is? If larger submarines have advantages like improved stealth and more room for everything from provisions to munitions, why did the US shrink its SSN size from Seawolf to Virginia?
Years ago I asked that exact question to the people who worked on the boats in Groton. The answer was that this 2m difference in diameter required change to
everything in terms of hull production - from the layout of the workstations to the established procedures for quality control. Humans are always the biggest cost factor and human error is the biggest risk factor and most people have no idea just
how much of a factor until it hits them with the bill.
Economy of scale is everything:
- Skipjack (1956-1961) - 9,65m beam, 6 hulls built
- Thresher (1958-1967) - 9,63m beam, 14 hulls built
- Sturgeon (1963-1975) - 9,65m beam, 38 hulls built
- Los Angeles (1972-1996) - 10m beam, 62 hulls built
- Virginia (1999-...) - 10m beam, approx. 40 hulls minimum planned
- Seawolf (1989-2005) - 12m beam, 12 hulls planned
So it wasn't that larger hulls were too expensive.
Moving production from smaller hulls to larger hulls was more expensive and
specifically for the USN. Astutes (11,3m) are larger than Trafalgars (9,8m) because only 7 are made and there are no economies of scale involved.
Furthermore Seawolf was built only in Groton (GD Electric Boat) which already is limiting the cost of retooling to half. Virginia-class could be built at both Groton and Newport News like Los Angeles-class without retooling. The difference in production from Los Angeles to Virginia is in modularity of hull sections, but hull modules end up being made and joined together with the same control procedures as a single hull.
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There are other reasons why bigger hull is not always better.
Submarine hull has to move through viscous medium which requires force. That force has to be generated externally which translates to noise in medium, as well as internally which translates to the reactor, cooling and power transmission.
10m diameter is 314m2 area. 12m diameter is 452m2 area. But water resistance is also calculated from hull area and that same 100m cylindrical hull gives you 6280m2 area for 10m beam and 7536m2 area for 12m. That's
44% and 20% increase in section area and hull area respectively.
Active sonar returns follow the same principles as radar cross section being directly related to the reflecting surfaces. More hull is worse and statistically submarines are located with airborne active sonar at safe distances from surface vessels. As noise levels approach reliably ocean background noise, active sonar becomes the only option and that's where hull shaping becomes a factor - new German designs already have hulls optimized for active sonar reduction. Where that leads in terms of overall size in future submarines is a question for thorough quantitative analysis, not an internet post.
China's nuclear sub fleet should be about sneaking into the West Pacific and the Indian ocean to pick out US assets. If the US imposes a distant blockade, its vessels will be spread thin since it doesn't have enough ships for such a task. That is what you want to see as a sub. To engage carrier groups you need missiles.
Soviets used missiles because technology gap and higher noise levels prevented them from getting close enough to use torpedoes. They also used
multiple submarines and waves of bombers to exhaust the defenses of carriers approaching
Soviet-controlled waters and airspace. It was always defense in depth at sea. If PLAN contests USN carrier groups it will be close to enemy waters or in international waters at open sea. They will be as exposed as USN and at a weaker position.
For every group of 3-4 submarines that is necessary to credibly threaten an USN carrier group with saturation strike there's one large sub with heavy long-range torpedoes that is both a much bigger problem for USN and much lower cost for PLAN. No matter how effective active sonar becomes in the future the problem is still orders of magnitude more complex than countering missiles with currently available technology. To paraphrase the most amazing woman of all time:
when enemy goes high, we go low.
Russians lag behind USN in all possible metrics so they utilized the advantage that physics provides and developed the Status-6 supertorpedo and Khabarovsk-class submarine.
Russians predictably went overboard but PLAN only needs to match it half-way to become a credible threat. And if we think AShBMs with a glider warhead then submarines are superfluous.
The resulting SSN is one that is less optimized as a high performance SSN-killer,
Seawolf wasn't a SSN-killer. Seawolf was a Bastion-penetrating SSBN-killer that was capable of matching
perceived Soviet solutions to American advantages in sonar and silencing.
When Soviets learnt through espionage about the level and nature of technological gap between them and the US they realized that to close the gap will take 1-2 decades with no guarantee of success. During that time they had to have some options as well as backup plans and from those emerged high performance submarines like Lira/Alfa, Komsomolets/Mike, Sierra etc. If Americans could hear them futher Soviet made sure that it wouldn't matter because no American torpedo could catch Liras which led to huge modernization program for Mk48. Komsomolets could dive twice as deep as American subs and if Soviets didn't start catching up in silencing and sonar thanks to the machines they were buying from the west, they'd probably develop dedicated titanium-hulled hunter subs with operating depths of 600m or so to better use layers of water and depth for hiding.
Seawolf wasn't designed based on the actual capabilities of Soviet subs at the time but what US intelligence thought Soviet subs could be capable of
when Seawolf entered service. Seawolf was USN future proofing for Improved Akula (Project 971M) which would enter service around that time and had noise levels of Improved Los Angeles.
It also was designed specifically to operate at longer periods of time than the usual Sturgeon/LosAngeles missions and with more tactical options available. If not for that USN would order a Virginia, just without all the littoral/spec-ops profile. They would anyway as there was no plan to ever build more than 30 Seawolf-type SSNs out of a fleet of ~100 SSNs. Seawolf would replace Sturgeons and a smaller boat would replace Los Angeles in due time.
Hull size isn't a problem except for energy issues that affect the economy of reactor design, but I don't think PLAN will design 09V like a Seawolf because I don't think 09III is a Los Angeles. Seawolf didn't exist in a vacuum but was a high part of another hi-lo mix. A reliable, good performance sub produced in large numbers is of more importance than a lower number of very high performance submarines. No matter how good a submarine is it will always be found in the end which makes it at best a short-lived tactical victory. A large number of "good enough" submarines is a long-lived strategic freedom of choice. Once 09V enters service we might see plans for a "large payload submarine" 09VII but I think that will follow the Russian thinking of SSBN-sized hunter subs designed from the start for working with UUVs.
Also... isn't this a 09III/09IV thread? Oh no... it is! Emergency dive!