August 30, 2016

Scorpene's and other DCNS sub's anti-ship Exocet missile. Land attack?

The potent Exocet SM39 anti-ship missiles can be used on DCNS designed subs, including:

-  Scorpene conventionally powered attack subs (SSKs) (including India's Kalvari Class), 
-  Agosta SSKs (see below)
-  Rubis nuclear powered attack subs (SSNs)
-  soon to be launched Barracuda SSNs, and
-  other non-DCNS submarine types if they are fitted with the SUBTICS combat system.
-  Australia's future Shortfin SSKs will use a US Combat System, US missiles and torpedos and
   probably British mines. 

In future one might expect:
-  submarine launched Exocets to have a land attack capability like the surface launched Exocet 
   MM40 Block 3s or
-  will another much longer ranged French missile, the MdCN be relied on for submarine launched 
   land attack? 

Youtube A. From NavyRecognition, uploaded April 5, 2012. It demonstratrates the SUBTICS (Submarine Tactical Integrated Combat System). The sub is using an Exocet SM39 anti-ship missile (see youtube below) and a torpedo to sink a landing helicopter dock (LHD). 

Youtube B. Real footage of an Exocet SM39 missile. The uniforms look Pakistani Navy(?). Hence the submarine is an Agosta - with a narrower bow than a Scorpene.
-  The SM39 (submarine-launched) Exocet (B2 Mod 2) is housed inside a water-tight launcher capsule. The capsule is ejected from the submarine's torpedo tube at a substantial depth, which makes it particularly suitable for discreet submarine operations. On leaving the water, the capsule  splits and drops away (31 seconds into the youtube) and the missile's motor is ignited.


Japanese Submarine Tactics - Deep Diving

This Submarine Matter's article is mainly about Japanese submarine tactics and practices. Contrasts with Australia's Collins practices are drawn. 

In Comments August 27-29, 2016 S, Josh and Anonymous provided details and comments regarding Japanese submarine tactics. I will leave S’s additional Comments on former Defence Minister Nakatani to a later date on changing Japanese defence-foreign policy. I have altered some of the original Japanese translation for clarity.

Japanese Submarine Tactics

According to the ex-Vice Admiral, Masao Kobayashi (with long experience of submarines) the Japanese submarine combat policy is “after firing torpedoes, dive deeper and faster.” He also said AIP (Soryu Mark 1) submarines must return to their base after consuming their oxygen (propellent for the AIP), while the advantage of Lithium-ion Battery (LIBs) Soryu Mark 2s and new class submarines (see SORYU TABLE) do not need to return to base.

After firing their torpedos, Japanese submarines will dive very deeply at maximum speed to avoid enemy counter attacks. Japanese submarines can dive deeper [maybe 600+m] than the crush depth of average torpedos. If the maximum speed of LIBs-Soryus is 4-5 knots faster than that of AIP/LABs-Soryus, then LIBs-Soryus can reach maximum submerged depth vital seconds earlier than AIP/LABs-Soryus. This may considerably improve the survival rate for LIBs-Soryus in combat.

The relatively strong steel hull of Japanese submarines [no Titanium used] enables application of these hit and run tactics. This is one of the reasons for hesitation in technology transfer to customer countries [Pete Comment - Australia was seen as a secure recipient of steel details but no Japanese transfer to India was considered]. The decision of full technology by Japanese government [to transfer to Australia] shocked Japanese Navy (JMSDF) members, submariners and engineers. The Japanese writer think Japanese are relieved, especially after the worldwide leakage of Scorpene technology.

As the defense strategy of Japan is exclusively defensive, Japan adopts a combination of submarine and other effective measures such as maritime patrol aircraft, including P3-C Orions and Japanese designed P-1aircraft. [Japan also heavily utilises fixed undersea “SOSUS” (really acoustic and more modern SeaWeb sensor types) along Japanese submarine patrol routes to support its subs (from the Japanese home island chain down to northern Luzon) – see “Fish Hook” Map]

Various factors such as geopolitics, geology, overseas deployment of troops, the domestic situation and defense policy of Australia are different from those of Japan. This is reflected in the nature and operation of submarine of the two countries.

Japan’s Sub Maintenance Philosophy is Different Than Australia's - Perhaps Resulting in  Different Tactics

A Japanese writer advises - All equipment inside Japanese submarines can be disassembled into small parts to allow the parts to be taken through the hatches in order to avoid hull cutting. Hull cutting causes reduction in a sub's near perfect roundness therefore weakening the hull. No recent Japanese submarines (centering on the operational Oyashios and Soryus) have experienced hull cutting. An earlier Harushio class sub called Asashio was cut into [Pete comment - Asashio was SS-589 then converted to testbed submarine TSS-3601] for its AIP equipment trialling.

The Japanese writer advises - in the Collins-class submarine, a rectangular cut [nicknamed the “sunroof” at the top of the hull near the stern] is conducted for [the frequent need for] repair and overhaul of the diesel generators. For Japanese submarine maintainers this is astonishing [as repair/overhaul is rare in its 17 year average life subs]. As the operational depth of the Collins may be as shallow at 200m, such “sunroof” cutting may be possible/acceptable. If true, does this limited Collins depth performance mean it is better suited to surveillance rather than fighting enemy submarines?

A Caution That the Japanese Full [mid 20s knots] Speed Has Limitations

Josh commented - I wouldn't expect the top speed mid 20s knots to be that significantly higher on the new [LIBs] design because in addition to using up more power this would require a dramatically more powerful [diesel] engine as well. The logarithmic relationship of power to speed; applies even more to the power of the engine than it does to the power storage capacity. 

High underwater speed in a diesel-electric (D/E) sub is only good for running away in a bad situation. Nukes can use it to actually change theaters. D/E designs generally hit a wall of cost-vs-benefit at ~20 knots and I wouldn't expect this to change despite the switch to LIB vice LAB/AIP: fundamentally even a D/E with all its diesels going is generating an order of magnitude less energy than an SSN and they can't afford to waste energy or likely even weight on a 25-30 knot capability.

S, Pete, Anonymous and Josh

August 26, 2016

Japanese Political, New Soryu and Torpedo Issues

Comments by Japanese friends, in July and August 2016, provide a whole body of insights and details little discussed in the submarine Anglosphere.

New Japanese Defence Minister Inada. Nakatani demoted?

In early August 2016 Japan’s conservative Prime Minister Abe appointed a like-minded conservative as Defence Minister. She is Tomomi Inada. Too early to tell what impact she will have. She is considered highly nationalist by China and some other regional neighbours. “Many political observers in Japan believe that Abe is grooming Inada to be his successor…”
I don’t know if former Defence Minister Nakatani has been demoted? If so, was it due to not selling the sub to Australia?

Sub size and sonars

Gleaned from Comments (27/7/16 12:05) from ex-Vice Admiral, Masao Kobayashi (SHIPS OF THE WORLD, from 2016, No.9) along the lines that generally the larger the submarine the more powerful and effective its sonars. This places larger, reactor powered, submarines at the top of the sonar effectiveness tree (particularly for more commonly used passive sonars). The large SSKs, like the Soryu and future Shortfin, would rate highly. Small SSKs (eg. TKMS Ula class and Type 210mod) not so much.

SORYU TABLE (with earlier Oyashios) as at August 26, 2016
Build No
MoF approved amount ¥ Billions & FY
Laid Down
5SS Oyashio
8105 Oyashio
SS-590/ TS3608
¥52.2B FY1993
LABs only
 Jan 1994
Oct 1996
Mar 1998
10 subs
¥52.2B per sub
LABs only
 Feb 1994
Mar 2008
Soryu Mk 1
¥60B FY2004
Mar 2005
Dec 2007
¥58.7B FY2005
Mar 2006
Oct 2008
¥56.2 FY2006
Feb 2007
Oct 2009
¥53B FY2007
Mar 2008
Nov 2010
¥51B FY2008
Mar 2009
Oct 2011
No 21SS built
¥52.8B FY2010
Jan 2011
Oct 2013
¥54.6B FY2011
Feb 2012
Oct 2014
7 Mar 2016
¥54.7B FY2012
Mar 2013
2 Nov 2015
Mar? 2017
¥53.1B FY2013
22 Oct 2013
Nov? 2016
Mar? 2018
¥51.7B FY2014
Mar 2019?
27SS First
Soryu Mk 2
¥64.3B FY2015
LIBs only
28SS  Second
Soryu Mark 2
¥63.6B FY2016
LIBs only
Mar 2021?
29SS First of
New Class
¥76B FY2018
LIBs only
Table courtesy of information provided to Submarine Matters. LABs = lead-acid batteries,  AIP = air independent propulsion, LIBs = lithium-ion batteries. ¥***B = Billion Yen.


[Pete Comment - The budgeting for the Japanese Ministry of Defence (MoD) is single year and multi-year depending on the documents. The Board of Audit (BoA) and Ministry of Finance (MoF) need to be convinced that ongoing or higher funding is needed for MoD's new submarine requests. The conceptual complexity of these requests is something MoD needs to constantly explain to MoF and to other relevant branches of Government.] 

Gleaned from Comments The non-AIP Soryu Mark 2’s (27SS onwards) and follow-on class will paradoxically have some structural similarities to the non-AIP Oyashios that preceded the AIP Soryu Mark 1’s.

The Oyashios themselves are undergoing life extension, including combat system upgrades, to bring Japan’s operational submarine numbers up from the existing average of 16 up to 22 (to meet increasing strategic threats to Japan). (24/7/16 11:35 AM)

Gleaned from Comments (on 21/8/16 3:30 PMIn the FY 2018 budgetary request, the Japanese Ministry of Defence (MoD) will request 76 billion Yen (0.99 billion AUD) for the first of the New Submarine Class (29SS) which will be Commissioned? “End of FY 2021” [that is in 2022?]. 29SS will be equipped with an improved sonar system and will be more silent/stealthy.

Comments gleaned May 2016 to August 2016

New Snorkel Budgeting Details

[Pete comment - Japan is perfecting a new snorkel system that is effective in the higher sea states (eg, storms) that are common in the Pacific.]

(12/5/16 2:19 PM) The snorkel generation system which MoD will use for Soryu Mark 2s (27SS and 28SS) is to be consist of a snorkel system and diesel generator. This terminology is rather difficult to understand, because the snorkel system does not generate power. But, this odd terminology has important meaning in the MoD budget and tender system.

27SS budget complexities

A competitive tender is applied for purchasing the diesel generator, because it is general equipment. In contrast, an optional contract can be applied for purchasing the snorkel generation system, according to related law [known as Cabinet Order on Budgets, the Settlement of Accounts, and Accounting (Chapter VII), Article 102-4, (iii)]. The suppler of snorkel generation system can select diesel generator as part, and consequently MoD can effectively exclude undesired diesel generator, I think.

The MoD may explain the increased budgets for 27SS and 28SS to the Board of Audit (BoA), but BoA will not accept the increased budget [merely] due to the price of LIBs. If 27SS and 28SS are not equipped with the new snorkel generation system, the floating [elastc sound reducing] deck and new sonar system, the price of 29SS which utilises these systems and new [G-RX6 see above] torpedoes will be nearly 80 billion yen. This is too expensive. [Pete comment - This quite confusing logistical budgeting situation will be clarified over time.]

Higher LIBs performance at higher cost

The new propulsion systems for LIBs-Soryus (27SS and 28SS) are more expensive (1.1 billion yen) than those for LABs-Soryus (0.9 billion yen). TMEIC (Toshiba Mitsubishi-Electric Industrial Systems Corporation) won the competitive tender of the propulsion systems against the conventional supplier, Fuji Electric Co., LTD.

It is expected the new propulsion systems are much more powerful than those for LABs-Soryus. LIB Soryus 27SS and 28SS will have a higher maximum speed than previous Soryus (reliant on LABs).

This is assuming
i)    increases in numbers and energy density of battery modules are both +50%,
ii)   maximum speed of submarine is proportionate to cube root of total capacity of batteries,
iii)  hotel loads at maximum speed are same for LIBs and LABs Soryus.

G-RX6 - Future Heavy Weight Torpedo

It is not clear whether the FY 2018 budget for the first of the New (post Soryu) Submarine Class 29SS includes the new torpedo, G-RX6, cost or not. If the cost of the G-RX6s is not taken into account for this budget request, this will present a budgetary problem. The 29SS, if equipped with G-RX6s, will too expensive (eg. 80 billion Yen). 

Judging from the budget status for development of the G-RX6, the development has nearly finished and 29SS can be equipped with G-RX6s. It is expected the 29SS will show much superior performance to current AIP Soryu Mark 1s (16SS to 26SS), because 29SS is 50% more expensive than 26SS!

-  See Japan is developing the Heavy weight [G-RX6] torpedo (HWT) for submarine, in order to oppose highly efficient surface warships and submarines. The HWT hass an advanced [Torpedo counter counter measures] TCCM function, and is excellent in detection, tailing, and the performance in deep and shallow ocean. The TCCM capability reduces or eliminates the effect of enemy ship's or submarine's decoys and acoustic jamming. [Pete comment: It is strongly assumed Japanese HWTs share technology with the US Mark 48 eg. in TCCM and  deeper/shallower performance.]

Pete and Japanese Friends

DCNS now warned on document leak by Australia's Defence Industry Minister

Comment: All pretty self-explanatory and perhaps expected.


1.  Uma Patel for Australia’s government financed ABC News, August 26, 2016, reports :

“Defence warns French company to keep submarine designs safe after India leak”

“The Defence Department has warned the French shipbuilding company building submarines in Adelaide to keep designs for the project safe.

Defence Industry Minister Christopher Pyne ordered the warning be given to DCNS — which won the $50 billion bid to build 12 submarines in April— after 20,000 pages of plans for their project in India were leaked.

There has since been discussion about whether the company was hacked. The Defence Department has told DCNS Australia wants the same level of protection as the United States [see Voice of America article] gives for information on Australia's submarines

The confirmation comes just days after Mr Pyne [and Prime Minister Turnbull] downplayed the leaks, saying he had received advice from the Department of Defence that the incident had "no bearing on the Australian Government's Future Submarine Program".

In a statement earlier this week, he said that the "program operates under stringent security requirements that govern the manner in which all information and technical data is managed now and into the future".

"The same requirements apply to the protection of all sensitive information and technical data for the Collins class submarines, and have operated successfully for decades," the statement continued.

But this morning on Channel Nine he conceded the leak was "embarrassing" for DCNS and the Indian Navy.

DCNS also issued a statement earlier in the week, saying that "French national authorities for Defence security will formally investigate and determine the exact nature of the leaked documents".

"The matters in connection to India have no bearing on the Australian submarine program, which operates under the Australian Government's arrangements for the protection of sensitive data," it added.”

2.  Russia Today, August 25, 2016 reports: "...The source went on to state that the documents seem to have been stolen in 2011 by a former French employee who had been fired in India while providing training on the use of submarines..." 


August 25, 2016

Who Might Gain From the Leak of DCNS Scorpene Documents?

I'm wondering what entity might conceivably gain from the leak of 20,000+ DCNS documents?

1. The leak would have damaged DCNS' reputation in India.

2. The weight of Scorpene technical details revealed might impede sales of Scorpenes.

3.  The leak has not helped DCNS' reputation in Australia.

4.  Substantial equipment types in the Scorpene also will exist in the Australia Shortfin, according to
     DCNS. So the leak also isn't helping Shortfin sales.

What do points 1 to 4 have in common?

There are two high value selection processes going on which still haven't been fully nailed down legally. These are:

- India's Project-75I and

-  Australia's SEA 1000. Australia selected the DCNS Shortfin but all the legalities are not yet fully
   nailed down. Also the US Government needs to be satisfied that the sensitive US combat
   system is being securely integrated (by Lockheed Martin or Raytheon). The integrator was to be
   decided soon - in 2016. High US confidence in the prime foreign contractor (currently DCNS) is
   implicit or explicit.

So what entity is well known to be a competitor in India's Project-75I?

Japan's fewer Submarine Leaks and High Strategic Threat Connection

With the DCNS document leak still in high drama one thing is becoming clearer. Japan very probably can keep its submarine secrets more secure. This is, in part, because Japan has entrusted its secrets to fewer entities: 
-  some submarine secrets to Australia (for the SEA 1000 competition that Japan lost), and
-  perhaps some to the US, likely for torpedos and other combat system components. 

Basically the more copies of secrets you distribute (to more countries) the more likely leaks will happen.  

One pressing reason Japan tightly holds its secrets is the high strategic threat that it is under. Russia and China represent significant threats (with powerful militaries) only a few 100 kms from Japan's major cities. 

North Korea probably represents a much higher threat that may elude MAD assumptions, making that  country difficult to place. North Korea represents a unique blend of nuclear menace under the, so far, absolute control of the insular and Pharaohic, Kim Dynasty

North Korea's latest piece of brinkmanship has been to launch an SLBM in the direction of the Japanese home islands (yesterday (24 August 2016). The SLBM was no doubt programmed to fall short but Japan would not have known that beforehand for sure and down range mistakes can happen. See lucky flight below. 

Unlike some previous claimed North Korean SLBM tests the extended flight of this 24 August 2016  test was very likely tracked by satellites (with electro-optical, radar and infrared sensors). The Russian origins of this KN-11 SLBM suggests what cannot be publicly admitted, that Russian contractors have been helping develop and test this missile for North Korea. (Map from The Japan Times).

Japan, by nature, is very reticent about mentioning scenarios or methods of pre-emptive missile strikes against North Korean ballistic missile threats. North Korea likely assumes a pre-emptive strike would come in overwhelming nuclear force from US submarines or perhaps even from China (to hose down the likelihood of WWIII).

Unfortunately the possibility that Donald Trump might win the Presidential Election (on November 8, 2016) provides Japan with no assurance about what kind of deterrence a Trump Administration would exert against North Korea.

(Photo, specifications, South Korea's KSS-III (Jangbogo 3) courtesy NavyRecognition May 2016)
Displacement (surfaced): 3,358 tons, Displacement (submerged): 3,705 tons
Length 83.5m, Beam 9.6m
Crew: 50
Maximum speed: 20 knots
Cruising range: 10,000 nm
6 vertically launched SLBMs [likely conventional warheads, initially]

[Probably around 16 torpedos, mines, anti-ship missiles.]

South Korea was more forthcoming in late May 2016 when it released news about a project to develop an SLBM for South Korea's future class of submarine - the 3,000-4,000 ton Jangbogo-3 (also known as KSS-III or KSS-3). Japan would also be considering submarine launched land attack cruise (and maybe ballistic) missiles. Japan may also desire parity with a South Korean submarine launched missile capability for its own sake. Japan and South Korea are neither enemies nor friends.

So Japan is quietly worried and would be keeping its future capabilities quiet.

I'll write on projected improvements to Japan's Soryu class and follow-on class submarines tomorrow.


DCNS Leak Drama - CEO DCNS Australia on design similarities of Scorpene and Shortfin

The DCNS Scorpene (above). Click on image to make larger/readable. 
Note the Scorpene's similar shape to Australia's future DCNS Barracuda (below). Major similarities between the Barracuda SSN and the Shortfin SSK derivative will be in hull shape and pressure hull steel. (Diagram courtesy of DCNS).

Computer modelling, which is constantly used by commercial and strategic competitors (think design bureaus in China and Russia) can heavily compensate for the size difference between Scorpenes and Shortfins. This allows competitors to register similar characteristics and vulnerabilities. 


The massive leak of 20,000+ pages of DCNS Scorpene documents reported overnight is of high value to DCNS's commercial competitors and/or strategic value to competitors of Scorpene owning countries. Scorpene owners are Malaysia, India, Chile and Brazil (once Brazil’s 4 Scorpenes and 1 nuclear Scorpene (SN-BR) are built). The Scorpene’s much smaller size (up to 2,000 tonnes submerged) might have been expected to make them very different from the (4,500 tonnes surfaced) Shortfin-Barracuda SSKs that Australia is buying.

Regarding the similarity of the Scorpene and Shortfin designs it is significant what Sean Costello (CEO DCNS Australia) stated in ASPI's The Strategist on 8 April 2016. He wrote: 
"The main area where Barracuda design references were not used was in the area of the electrical system (batteries and voltage), power generation (induction and diesel generators) and propulsion (main electric motor). In these systems the design reference comes from the Scorpene class of diesel electric submarines, or from an existing submarine technology within DCNS. Existing technologies are re-used in all systems in the Shortfin Barracuda Block 1A. System by system, the whole ship performance is validated and the design loop closed."

If the now known Scorpene characteristics can be related by computer modelling (or directly by Costello of DCNS) to the Shortfin this does not bode well for the Shortfin's future stealth. Computer modelling, which is constantly used by commercial and strategic competitors (think submarine design bureaus in China and Russia) can heavily compensate for the size difference between Scorpenes and Shortfins.

Also the later Scorpene models (for India and Brazil) were designed over the same period (2000-2010) as the DCNS Barracudas (from which the Shortfin derives).

Major similarities between the Scorpene and the Shortfin will be in hull shape and pressure hull steel - which together influence acoustic and magnetic signatures that an enemy looks for.

BTW - The document leak might also give Pakistan’s competitors insights into Pakistan’s five DCNS Agosta class completed 1979-2006. The Agostas completion overlapped with the first two Scorpenes completed for Chile in 2005 and 2006. Scorpenes and Agostas also share portions of the French SUBTICS combat system (see my details on SUBTICS for Scorpenes and Agostas here).


Quartz India, August 23-24, 2016 reports :

“Over 20,000 pages of top-secret data about India’s mega submarine project leaked, says The Australian”

“India may have a suffered a huge strategic setback, particularly on the naval front.
Some 22,400 pages of data related to the six Scorpene-class submarines that the French government-owned company DCNS was building for the Indian Navy have been leaked, The Australian reported on Aug.24. “The stunning leak… details the entire secret combat capability of the six Scorpene-class submarines..,” the report said.

The leaked documents list out the frequencies at which the submarines gather intelligence and the levels of noise the subs make at various speeds, the news report said. They also contain information on the submarine’s diving depths, range, and endurance, besides its magnetic, electromagnetic, and infrared data.

It is not yet clear how, where, and to whom the top-secret information was leaked. Nevertheless, India’s naval strategies may suffer grievously following this development, particularly if the leaked documents are made available to India’s rivals Pakistan and China.

Fallout in Australia:

In a major embarrassment for DCNS Australia’s Uma Patel and Stephanie Anderson for ABC News Online, August 24, 2016 report“French submarine builder information leak has 'no bearing' on Australia, Malcolm Turnbull says”. Prime Minister Malcolm Turnbull has downplayed the effect of leaks from the French shipbuilder chosen to build Australia's next generation of submarines.


The Australian newspaper, August 24, 2016, reported :

"The US will be alarmed by the leak of the DCNS data because Australia hopes to install an American combat system — with the latest US stealth technology — in the French Shortfin Barracuda. If Washington does not feel confident that its “crown jewels’’ of stealth technology can be protected, it may decline to give Australia its state-of-the-art combat system

...DCNS Australia this month signed a deed of agreement with the Defence Department, ­paving the way for talks over the contract which will guide the design phase of the new ­submarines.” See WHOLE ARTICLE in The Australian.


Leak of DCNS Documents Drama continues in France, India and Australia

Further to the Submarine Matters article of August 24, 2016 Cameron Stewart for The Australian, August 25, 2016 reports (in part):

“…Independent South Australian senator Nick Xenophon said the [Australian] government’s response to the leak was “woefully inadequate” and it should consider suspending negotiations with France until the issue was resolved. “For the minister [of Defence Industry, Christopher Pyne] to say that the leak of internal documents from French company DCNS in relation to their Indian submarine contract, ‘has no bearing’ on the Australian program is extraordinary,”

Senator Xenophon said. “This leak is extremely concerning, and Minister Pyne cannot make such glib statements without finding out exactly what happened with this leak.”

… Australian Strategic Policy Institute head Peter Jennings said DCNS would have work to do to convince Australia and the US that it had the highest levels of information security surrounding the Australian submarine project.” See WHOLE ARTICLE in The Australian.

August 24, 2016

Why is the 16 SLBM Columbia class SSBN-X larger than a 24 SLBM Ohio?

Question:  Why is the 16 SLBM Columbia Class SSBN-X larger than a 24 SLBM Ohio? (see Table way below. Displacement and Beam is larger).

Cutaway of SSBN-X from page 9 of 2016 Report to Congress.


The larger the submarine the smaller the influence of its weapons on displacement and length.

The displacement of the future SSBN-X's 8 fewer SLBMs (16) than the Ohio’s 24 and dimensions for 8 fewer tubes doesn’t mean the SSBN-X is 33% less in displacement/length/beam. 
-  Beam always needs to be the same or greater to accommodate the length of the 
-  The Ohio’s 24 SLBMs were a break in the decades old pattern (page 36) of 16 SLBMs.
-  The most pessimistic predictions (of many opposing Russian SSBNs) didn't 
    materialise. (see comparative Table below).
-  The USN must be calculating that threat, stealth and budget means 12 x 16 SLBM 
    SSBNs is adequate for the 2030-2080 SSBN-X era. 
-  But more Common Missile Compartment (CMC) quad-packs and more MIRVs
   per SLBM can always be retrofitted if need be.

The SSBN-X crew (at 155) remains the same because all the requirements needed to maintain the submarine and its SLBM payload involve the same crew specialities, damage control and other fixtures for 16 as they do for 24. There may even be a need for a few more crew in, say 22 years time, to improve stealth.
-  the task of safely operating the reactor requires many crew no matter how many missiles are carried

An inbuilt capacity to absorb improvements and stealth over the 42 year life of SSBN-X involves room to grow into spaces left empty in the hull. Much of this is expanding the computer power by adding more memory and other processing on spare racks in the combat system database. See “must be fitted with the most up-to-date capabilities and stealth to ensure they are survivable throughout their full 40-year life span.”(# below), So more electronics and memory for future active stealth and combat system upgrades may take up much extra space-displacement.

Perhaps more decoys the size of HWT sized UUVs (if the 4 torpedo tubes are retained?).

The tubes for SSBN-X's SLBMs are the same 87-inch diameter as on the Ohio-class, but are a foot longer  -  leaving some margin for a future missile design. This explains the need for a space/displacement increasing Beam of 43 feet compared to the Ohio’s Beam of 42 feet.

The new reactor may be very slightly heavier and larger, with more 90+% HEU for the longer life between refuels (stretched from the Ohio's 19 year mid-life, to being sufficient for the SSBN-X’s whole 42 year service life).

SSBN-X and Ohio class Comparison Table

Measure/Replacement or Ohio
Ohio Replacement, SSBN-X, Columbia class
Ohio class
Number of SLBMs
In Common Missile Compartment (CMC) quad packs #
But just 20 after 2018*
Launch tubes
Same 87 inches SLBM launch tubes ***
Same 87 inches SLBM launch tubes ***
560 feet ***
560 feet ***
43 feet ***
42 feet ***
Larger,  20,815 tons “(as of August 2014)” submerged ***
Smaller, 18,750 tons submerged ***
Crews Blue/Gold
2 x 155 #
2 x 155
Years between HEU refueling
(service life) ***
About 19 *
Drive, propulsion
electric-drive propulsion train ***
pump jet, X-plane rudder#
mechanical-drive propulsion train*** bare propeller,
cruciform-H rudder
UK Successor and Vanguard classes
On UK Successor class    8 x Trident IIs, In Common Missile Compartment (CMC) quad packs # UK made warheads **
UK Vanguard class carry 16 x Trident IIs, UK made warheads**

* page 3 Ronald O'Rourke’s Navy Columbia Class (Ohio Replacement) Ballistic Missile Submarine (SSBN[X]) Program: Background and Issues for Congress, of August 18, 2016 CRS 7-5700 R41129 (5 MB PDF)
** page 4