[rdtsc]

> In particular, Russia is now in the process of testing a 40-ton nuclear-powered underwater unmanned vehicle (UUV) that could robotically deliver, across thousands of kilometers, a 100-megaton nuclear warhead against the coastal cities and ports of the United States.

Interesting. What kind of damage would that do. Maybe a few of those blowing up at the same time would cause a tsunami wave? It sounds like something out of Dr. Strangelove. Water is also good at dampening explosions, I'd think.

Aha, there is XKCD for this already: https://what-if.xkcd.com/15 . It turns out the wave created by one won't be like a tsunami wave as it will break too quickly. So maybe they'd need to stagger a few devices in a row.

Linked from there is a very thorough paper "Evaluation of Various Theoretical Models For Underwater Explosion" http://www.dtic.mil/dtic/tr/fulltext/u2/737271.pdf

[tgsovlerkhgsel]

I think that instead of trying to create a tsunami, it might be slightly more effective to drive one straight into a port/city, and detonate at the surface.

New York: https://nuclearsecrecy.com/nukemap/?t=a1c1cd0eeccb2488024ace...

San Francisco: https://nuclearsecrecy.com/nukemap/?&kt=100000&lat=37.747095...

[nerpderp83]

Why wouldn't you just use Fedex, DHL or an intermodal shipper?

[rdtsc]

You joke but they have an intermodal shipping container missile. You can buy it if you have some extra cash laying around:

http://roe.ru/eng/catalog/naval-systems/shipborne-weapons/kl...

[rdtsc]

Ah makes sense. So it is more about delivering it closer to the shore so it can't be as easily detected than creating tsunami waves as the main mechanism of destruction.

[jadedhacker]

I did some research on Operation Crossroads a while back. I'm not sure what the blast effect damage would be, but it would cause radioactive water to wash over the town. Several warships in the exercise were scrapped because they could not be cleaned as certain isotopes stuck to the metal.

EDIT: Of course, how much radiation exposure you're willing to tolerate is a risk assessment call, but it seems pretty unfair to the civilian population to take any significant increased radiological risk.

EDIT2: 100MT is the design yield of the Tsar bomba, the actual detonated yield was 50MT b/c the plane dropping it would not have been able to escape at the design yield. This is a very very big bomb if that capability were actually used. I assume smaller bombs would also be able to be used as well.

[cryptonector]

Part of the problem is that 100-megaton bombs are probably built with Uranium-238 tampers and are extremely dirty. To use even one of those would cause enormous problems for all parties including the one deploying it. It's not something you want to do.

I suspect these UUVs have no such tamper and a yield more in the 30-megaton range for this reason. These would still be more than enough to kill many millions each.

My guess too is that these wouldn't be detonated underwater -- not much rise above water would be needed to wreck havoc.

My biggest concern is that these would likely be dead-hand weapons, with many possible failure modes leading to attack.

We should be willing to share space-based early warning data and technology with the Russians to head off this crisis. Alternatively go back to the old fuzes, but sharing early warning satellite tech is easier.

[rdtsc]

> We should be willing to share space-based early warning data and technology with the Russians to head off this crisis.

That's interesting to think about. It makes logical sense at first, but I doubt it is realistic.

Thinking about it some more, it seems having a better detection capability means having a higher chance of shooting the missiles down. That can then be used by the aggressor to dampen a retaliatory attack. (Say we give it to Russia. They attack first. Then when we retaliate, they use our advanced system to know the trajectories of the incoming missiles and use that to shoot them down. Our retaliatory attack fails and we lose).

[mcguire]

100M ton Tsar Bomba, surface explosion just outside the Golden Gate bridge.

https://nuclearsecrecy.com/nukemap/?&kt=100000&lat=37.813996...

[jadedhacker]

I wonder at what depth a nuclear sub would detonate. It does seem conceivable that it might surface. The fallout model relies on the fireball touching land, so the part that is over water would have less impact. However, with a bomb that size, the water might consist of only a fraction of the total area.

[portofcall]

Think more in terms of killing a whole carrier battle group in one shot, or closing a major port (for a long time) due to blast damage and radiation. Larger bombs are diriter bombs, and detonating in water is pretty much the dirtiest use of a dirty bomb.

In short, this is a strategic terror weapon, an area denial weapon, and a radiological weapon.

[cryptonector]

Yes, quite. There's no tactical or even strategic value to this other than as a terror-based deterrent. Of course, all nuclear deterrence is terror-based to some degree, but weapons that can only really be meant to attack populations are more terrible than ones meant to attack military targets.

We saw this back during the height of the Cold War, where first very high-yield weapons were deployed due to lack of sufficient accuracy, then later these were replaced with lower-yield weapons as accuracy increased. These UUVs are a desperate move to make up for lower capability in other parts of the Russian deterrence strategy. They're scary indeed.

[caf]

There's no tactical or even strategic value to this other than as a terror-based deterrent.

Of course. It's explicitly a second-strike weapon: if it is ever actually used, it has already failed in its mission.

[marshray]

What makes water especially dirty for this purpose? It seems like more of the bad particles would be washed back out to sea than if they'd been dispersed as fallout dust.

[portofcall]

It might seem counterintuitive for the reason you described, but the problem with water and ground bursts, is that the entirety of the radioactive byproducts interact with large amounts of dense material. I’m a true airbursrs, the fireball doesn’t touch the ground, so the air itself is contaminated, along with material from the ground which is drawn up into the fireball through convention and blast effects. That’s still dirty, and in the case of the Tsar Bomba (50MT) catastrophically dirty. The total volume of affected material though is relatively low.

If you detonate underwater, all of fission byproducts, and unburned fuel comes into direct and prolonged contact with a large volume of dense material. In a shallow blast, gigstons of thst material are ejected into the atmosphere, while the rest remains underwater. It will be diluted, it a 100MT device is still going to produce horrendous and long-lasting effects.

That material will poison the underwater environment as it settles in the immediate area, and for km away as it dissipates. Worse, it will enter the food chain and be concentrated through progressive predation.

This covers the explosive (not radiological) effects of non-airbursts for some context! http://www.abomb1.org/nukeffct/enw77b2.html