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Comment by littlestymaar | Hacker News Reader

Nuclear arms doesn't need as much accuracy as other weapons though: when using a cruise missile or a glide bomb with a few hundreds of kilograms of explosives, you need metric precision to get the military effect, when the payload is a 100kt bomb, then 100m is accurate enough.

Unlike other bombs it must absolutely be 100% resilient to any kind of spoofing though, for obvious reasons, hence GNSS is a nonstarter for those when they are the default guidance system for other weapons (with backups, for cruise missile).

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> when the payload is a 100kt bomb, then 100m is accurate enough

Not accurate enough for counterforce. When a missile silo lid can withstand 600 atmospheres of overpressure, "close enough" isn't good enough.

It makes a difference for hard targets, see the new nuclear "super-fuzes."

It can take several warheads to destroy a missile silo with high probability, because even landing a little off-target can spare the silo. Greater precision means it takes substantially fewer.

https://thebulletin.org/2017/03/how-us-nuclear-force-moderni...

I don't really get this argument: if you have a metric precision munition in an ICBM then even an inert warhead is going to be enough to penetrate and destroy due to the kinetic energy coming from the hypersonic nature of the reentry vehicle (and even if kinetic energy itself wasn't sufficient, a conventional payload would be)

Nuclear bombs are useful because you don't need precision to get the effectiveness, but if you have the precision then why would you bother with the consequences of using nukes…

Not if the silo can withstand a direct hit from anything short of a nuclear bomb going off nearby. ICBMs aren't that precise- or they didn't used to be- and that's why you'd compensate for that with nuclear warheads. Or, alternatively, early ICBMs would have seemed nearly pointless to develop before nuclear weapons existed to put on them.

If a superfuze or a super-IMU means that you can kill one silo with one nuke, that is a huge improvement over the old status quo, where it was assumed to take several, simply because the CEP was larger than the radius at which they can destroy a silo.

If someone does have an conventional ICBM that can reliably take out nuclear silos that would be an even bigger deal.

Of course the US military has been working on conventionally-armed ICBMs: https://en.m.wikipedia.org/wiki/Conventional_Prompt_Strike

> Not if the silo can withstand a direct hit from anything short of a nuclear bomb going off nearby

But this kind of silos simply doesn't exist.

Yes you could theoretically imagine such a silo, but because the threat of a conventional bunker buster payload hasn't been very realistic when it comes to nuclear silos, they aren't designed to deal with such a thread and instead focus on protection against the kind of overpressure that is caused by an nuclear explosion occurring around.

My point was that nuclear missile development gets a blank check and I cited the over-six-figure intertial guidance units in 80's and 90's era missiles as an example of this.

I'm not sure what point you're trying to make here?

Accuracy is incredibly important because you don't put a nuke somewhere to kill people; you put it there to destroy infrastructure. More specifically nuclear missile silos, and bomb shelters (well, the people inside them.)

Reducing the CEP means you can use a smaller nuclear yield to get the job done, which is preferable for a number of reasons, including politics, but also allowing for more targets in a strike.

The very latest US ICBMs are suspected of having sub-100m CEP. CEP for ICBMs is "bad" enough that it is typical for planners to figure three warheads per target, but accuracy is rumored to be getting good enough where that is no longer necessary.

> you don't put a nuke somewhere to kill people; you put it there to destroy infrastructure. More specifically nuclear missile silos, and bomb shelters (well, the people inside them.)

It depends.

"Counter-force" strikes aim to destroy the ability to respond or attack with nuclear weapons, not infrastructure per se. So that's just silos, warhead storage sites, submarines in port, airfields, etc. The US is doctrinally counter-force for about half a century. This doctrine is also reflected in technological choices: lower yields and higher precision mean lower fallout, collateral damage, and fratricide when hunting for silos, but aren't that useful for city busting.

"Counter-value" strikes are pure destruction of cities and killing of people. Russia seems to have this doctrine [1]. This is a very inflexible doctrine, because you can't credibly threaten to execute a counter-value attack on the US over things that don't seem to be worth a response in kind (like a defeat in Ukraine). It's much cheaper though.

> The very latest US ICBMs are suspected of having sub-100m CEP

Apparently the precision is good enough for photos like the one on page 23 here https://www.osti.gov/servlets/purl/1557069

[1]: At least strategically. There is a hybrid strategy of targeting military-related infrastructure, which Russia seems to have adopted for less-than-strategic forces according to recent leaks https://www.ft.com/content/237e1e55-401d-4eeb-875b-03fe68f81... .

They do need very good IMUs though, because of their range and flight time: uncertainty in position increases with both of those.

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