[avar]

The US is peculiar with its nuclear policy in trying to guarantee immediate response, by contrast say the UK only has nuclear submarines at sea, and it's expected that there'll be nothing like an immediate response, rather the captains of those submarines will find out who nuked the UK and respond.

So the answer for deterrence purposes is you don't need to nuke anyone right away, immediate response is only one layer of the onion when it comes to nuclear deterrence.

[PhantomGremlin]

The US is peculiar with its nuclear policy in trying to guarantee immediate response

This doctrine is called "launch on warning". It hasn't been official US policy for 20 years[1]: In 1997, the Clinton administration changed the official policy away from launch on warning to one of retaliation after withstanding an initial first strike.

[1] https://en.wikipedia.org/wiki/Launch_on_warning

[avar]

I'm referring to the policy of still maintaining the systems necessary to launch on warning, past promises about how the systems will be used are just PR.

It's not like in a hypothetical scenario where Russia has launched hundreds of ICBMs at the US in a first strike scenario Trump (or any other president) is going to feel beholden to some promise Clinton made in the 90s.

The president has absolute power over when and how to launch nuclear weapons, and can do so at a moment's notice, as has been covered extensively in the media in the last year where people seemed shocked that the president had this power since they didn't like the new person in office, even though the power itself hasn't changed in more than half a century.

[pps43]

If you rely only on submarines for deterrence then you don't need satellites detecting launches in the first place. I don't think UK or France have (or need) that capability.

[avar]

That's not how it works. The US also relies on the ability to promptly respond to a first strike, which say the UK does not.

What I'm pointing out is that you've conflated two things. Just because one aspect of your deterrence is the ability to launch your land-based ICBMs within 30 minutes, that doesn't mean that the inability to do so (e.g. because you don't know who struck you) means that you're out of options.

Besides, there's no way someone could amass enough SLBMs in the Pacific to take out two aspects of the US's nuclear triad without the US knowing who owns those submarines.

[pps43]

I was trying to explain why it is more important for the satellites to quickly detect launches from land.

With SLBMs you have other options. You can have your attack submarine shadowing enemy's ballistic missile submarine, or surface ASW ships patrolling the area that can detect the first launch and try to sink the ballistic missile submarine before it can launch its remaining missiles.

[avar]

Sure, I'm just replying to your question of "Who do you nuke? [if you don't know who launched a missile against you]", which it seems to me is implicitly assuming that if someone nukes you you must nuke someone back right then and there.

That's nobody's nuclear posture, it's just a subset of the posture of the US, Russia, China etc.