Re: Question: DBF vs SSN

December 2008



Every so often, like clockwork, this question comes up and not much gets moved. I call ’em “36M-4R questions”, questions like “bring back the battleships”, women on subs/in combat/aboard ship, the draft, when two carriers overlap in Gulf deployments and somebody every time gets convinced we’re about to invade Iran, et cetera. These questions come up but don’t do much more than feed a bull session. I’m not much changed from my 2004 take on the diesels question, except to note the price of ASDS, we still say we’ll make things up in the outyears, and Taiwan still without new boats. Part of that post:

That cost-vs-capability drives us to a prisoner’s dilemma logic. If the less capable thing is six and a half bucks, the more capable thing is ten bucks, and you have eleven, you always pick the more capable thing. This is, however, a short term logic–if you figure out that the national value of six SSKs is more than the national value of four or two SSNs over the long term, then you make another decision. (Note that I say “national value” here, not “equivalence”–comparing the two directly may not be the correct measure to make.) Add in other things like a different structure for a different kind of ship, too.

Buying SSN vs. SSK requires a decision bigger than the first couple years of budget–and nothing that is in the POM outyears is recognizable by that time. When the Navy buys a gadget, they put a request in the budget that goes via the President to Congress, in a Politburo-style Five Year Plan. The next year’s money gets approved, and the “out years” at the end of that plan aren’t necessarily what happens the next year when we send another budget up to Congress again. So here lies another conundrum. We always say we make up the shortage in the out years, but there isn’t really a hammer to force a service to do so–and that’s probably not all bad, since it’s too long to react to changing technology or strategic situation.

A diesel sub can’t drive at ahead flank for two weeks, then spend three months sitting off the coast of mumble with no support. A nuclear-powered boat can. With thousands of miles between home port and your destination, that makes sense. Our diesels, before they got paid off, were forward deployed to save that time and gas–but it was still harder for them. Nuke aircraft carriers like having the sub sprint ahead. Diesels can’t do that well. With this lower capability, coupled with the prisoner’s dilemma, we stopped building diesels.

Taiwan wants subs, as their WWII U.S. handoffs (Guppy conversion, actually) are old old old, and they realize that an asset in the strait is better for them than a promise of a carrier later. They got a massive case of sticker shock…and then found out that several previous attempts at building non-nuclear subs in the US have been killed off.

So let’s say you’re not a submariner or a strategy guy and haven’t thought of this question before. Alternatively, you weren’t swayed by the inevitability of my deathless prose and want to work through this on your own. Here’s how I’d frame thinking about the question: by asking other questions.
What strategy does this support? What mix of the rest of the Navy and DoD determines this choice?
–What do you want to do with the SSKs, since you can’t steam one at flank across the Pacific and sit off the coast of mumble until the food runs out?
–If these boats are for the USN, how many ships or other boats don’t get built due to the resource move to diesels, since diesels cost a lot more than people assume–and you have to add in the cost of tenders, replenishment and forward basing since we need the offensive capability to move forward, which requires infrastructure. This hidden cost outside the hull’s cost can get appropriators into trouble. So can first-of-class costs. See the Collins price tag, or the reaction of the Taiwanese government when the cost to them became clearer. Also, the build cost of an SSN includes the fuel–a huge factor and a completely different way of looking at resource allocation. How many surface ships don’t sail as scheduled because the quarter’s gas money ran out for that group? How would it be done differently if you planned fuel cost over decades instead of months?
–Are you really saying “should we allow US yards to make diesel boats to rival the HDW export program”? If so, to whom and why?

An SSK is like an intelligent mine; a trump card, but tied to the supply chain and its need to recharge. An SSN is able to drop everything, race to station, carry more stuff, stay longer and move farther…and the comparison is essential because money is not unlimited and the missions aren’t as different as they would be if you were arguing more about an overall hi-low mix for the Navy ships.

Some previous discussions of the issue, which have useful comments:

Posted by Chap in Foreign Policy, Hard Power, Navy

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  • SeniorD

    Granted, a diesel boat can’t sprint ahead of a CBG or stay on station for weeks at a time. Goodness knows battery power is no match for nuclear.

    In contrast, a nuclear boat’s primary benefits are severely restricted in shallow waters (think China Sea, Western Med). Not much clearance, the shoals are ever present and even the boat’s sonar systems are hard pressed to get through the noise.

    Diesel boats are stealthy, superbly quiet and ideal for shallow water. That is where the fight will begin and the deep blue water advocates aren’t playing to diesel strengths.

  • DG

    Diesels are great for Taiwan – they are superb for interdicting shipping and controlling the sea in a restricted area. They are much less useful for the US. The Germans are supposed to build some very nice diesel subs – the Dolphin SSK used by Israel. A half dozen of those could really shore up Taiwan’s defenses.

  • Chap

    I’ve heard that argument and am not so sure that changes the game too much. The SSNs can go pretty shalllow. How shallow is the shallow end of the pool? Which areas can the SSK play where the SSN can’t, especially if you build the SSN to take shallow into account? For the Taiwan Strait scenario, wouldn’t it be better to have Taiwanese forces in place, like mine layers, instead?

    Sonar is as tough for an SSK as it is for an SSN. If the ‘fight’ begins in waters too shallow for SSNs, why is that? Is the endurance tradeoff worth it and why? How are you going to get the SSK there?

  • Chap,

    USNI’s Independent Forum is alive and well on this blog’s first week. Outstanding. What a country. Back to thinking about prospects for future bull sessions….

  • Byron

    That’d be my two cents worth, Chap. The “sonar conditions in the littorals” argument swings both ways. If if sucks for the nuke boat, it sucks for the diesel too. The difference, as you’ve said, is in endurance and range submerged at a steady 12 knots. In this case, quantity does not equal quality.

  • Chap

    Great initiative, Jim. Let’s have some more challenging questions!

    Quite frankly, I would have liked to see discussion on stealthy sensor placement and mine emplacement, since those two things can do missions that affect the impact of having a sub there or not there. Ferinstance, if you had a long dwell sensor suite that can move around and be sneaky, does this mean you change the required mission set for the sub force? Does that affect acquisition if so? That kind of stuff.

  • Chap Thanks! Looks like I have a question for next week and will be sure to give you the h/t.