Saturday, September 1, 2012

SSBN(X) - Smaller Without Being Smaller

The Navy is in the process of developing a replacement for the Ohio class Trident ballistic missile submarines (SSBN).  The next generation ballistic missile sub (SSBN[X]) is described in the recent CRS report (1) as containing 16 missile tubes versus 24 in the Ohio class.  The tubes will be the same dimensions.  The sub’s beam and displacement will be comparable to the Ohio’s.  So, although containing one third fewer missile tubes the SSBN(X) will be the same size as the Ohio.  Throw in presumably smaller, more efficient nuclear plants, greater levels of automation, and the likelihood of reduced (or eliminated – though that seems unlikely) torpedo spaces and one might be tempted to reasonably conclude that the resulting sub should be smaller than the Ohios.  Apparently, one would be wrong!

This seems totally illogical on the face of it and I don’t understand it.  I’ll keep looking into this.


(1) Congressional Research Service, “Navy Ohio Replacement (SSBN[X]) Ballistic Missile Submarine Program: Background and Issues for Congress”, Ronald O'Rourke, April 5, 2012

14 comments:

  1. Conavops, it is very interesting that the SSBN(X) would not be smaller. The fewer missiles make sense in light of START restrictions and the ability to spread strategic assets across a larger number of ships. One statement you made piqued my curiosity. You suggested an eliminated torpedo space. Is it proposed to eliminate the ship's only self defense system?
    Your arm-chair admiralty is great. Keep up the good work!

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    1. Anon, thanks for stopping by!

      I have no idea whether fewer missile tubes per sub make sense or not. Hopefully, someone has carefully examined the issue and decided from an operational and strategic basis that fewer tubes are needed. Unfortunately, everything I've read suggests that the reduction is purely a cost savings exercise.

      Also, if your comment that strategic assets are going to be spread across a larger number of ships refers to having more SSBN(X) subs than our current number of SSBNs, you should be aware that we are going to build 2-4 fewer SSBN(X)s than we have now. So, we'll have fewer missile tubes spread over fewer subs. Again, that seems to be a purely cost reduction move.

      Various articles have been published in the Naval Institute Proceedings calling for reduced or eliminated torpedo spaces. The rationale was that an SSBN avoids combat and, therefore, doesn't need torpedos. While this is tactically stupid, the cost savings may trump tactics. Personally, I hope this doesn't happen but we'll have to wait and see.

      Thanks!

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    2. When I think about this, I wonder what could be done with the space freed up by such a reduction of missile tubes. Then I start thinking about what the Navy has done in the past when the reduce the number of missile tube in the fleet. The results seem to point in an obvious direction.

      G Lof

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    3. Well, I'll admit you have me stumped. I have no idea what you're hinting at about a use for the space. The only thing I can even remotely think of is the use of two missile tubes on the SSGN conversions as special ops swimout chambers and that wouldn't seem to appy, here, since the tubes won't be installed to begin with. Care to elaborate on your idea?

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    4. CNO, just because the SSGN used existing tubes to carry the SO equipment, does not mean that future SO submarines need to do so. The Jimmy Carter carried it's equipment in a special launching bay. Given the one size fits all mentality that current effects the Pentagon's bureaucrates, it would not surprise me if they try and build a combined SSBN/SSGN.

      G Lof

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    5. GLof, now that's an interesting thought! The original Ohios had 24 tubes which would mean that there's space for 8 guided missile tubes which would provide for 56 Tomahawk missiles. The converted SSGNs can carry 154 missiles.

      Is it wise to risk one leg of the strategic triad in an SSGN role? I'll have to ponder that. Do you consider the risk worthwhile?

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    6. I am not so sure that the trident role and the Tomahawk role differ that much. Both operate basically in a hide until needed mission profile.

      The part that does make me wonder is the Special operatiom mode. This may require the submarine to expose itself more than the other roles. If they develop a truly successful mini-sub to transport the SEALs from far of shore, then it could make such a multi function submaine viable.

      G Lof

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    7. In a sense, you're correct, however, one major difference is the firing ranges allowed by each weapon. Trident D5s have a range of 7000 miles versus 1000 miles for Tomahawk. So, in order to strike inland targets in China, for instance, the sub would have to launch Tomahawks from a few to several hundred miles depending on how far inland the target is. That puts the sub squarely in the heart of the A2/AD zone and the max ASW opposition effort. That's a lot more risk than launching a Trident from a few to several thousand miles away.

      In a war with China (presumably a major, major conflict) which could go nuclear, I'm not sure we'd want to risk our stratgeic assets to that extent. What do you think?

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  2. A reason I can think of why the SSBN(X) would be as large as an Ohio is hull silencing. The Ohio design is regarded by many as the quietest class of submarine out there, but the technology is over thirty years old. A new design would have more elaborate means of eliminating and containing acoustic energy. That usually means more hull structure.

    The same with the sonar. Newer SSNs like the Seawolf and Virginia are larger partly because their sonar arrays are more extensive. Old SSNs had only a bow dome and a clipped on towed array. Newer boats like the Virginia have reelable towed arrays that are contained within the hull, and large side mounted wide aperture arrays. All that adds to the overall size. I don't know how extensive the sonar suite of the SSBN(X) will be, but the Ohios were given a sonar suite nearly equal to what was being put into a Los Angeles boat at the time.

    WireguidedMarine

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    1. Fascinating ideas!

      Regarding the sonar fit affecting the size, the Virginias are 377 ft long versus the Ohios at 560 ft. If the new SSBN(X) were reduced in length by 1/3 they would be 370 ft which would give them the full Virginia length to fit that sonar suite. Of course, maybe they're going to get more than the Virginia?

      I think we're still missing the rationale for the Ohio length on a sub with 1/3 less "stuff" in it. Good thoughts, though!

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  3. Just as a side note to this story, the UK which is building a new class of SSBN with a reduced capacity of 8-12 Trident D5 missiles,to replace the Vanguard class (16 capacity Trident D5 missiles) from 2028 onwards, is also anticipated to be the same 150m in length and a similar 16,500 tonne displacement to the Vanguard boats.

    Very strange.



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    1. One other note of similarity is that the UK and US are using a common missile tube module. The tubes are being built into the hull modules rather than added after the fact. A full scale mock up has already been constructed to prove out the concept.

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    2. One of the theories I have about the UK replacement boats being the same size as the Vanguards, despite carrying a smaller weapons load, is that the RN want to make the boats more comfortable for the crew with individual bunks for each crew member, also extra accommodation will be needed for female crew members, who will be allowed to serve on Subs.

      If the RN can improve the living conditions on these boats for the 3mth patrols, it will go along way to help recruitment and retention in the service.


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    3. The on-board tennis court, alone, will add 100 ft. Plus, the extra closet space needed for female crew to store all their shoes is going to be significant!

      Oh, take it easy people. Just having some fun!

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