Does the US Navy’s mission require it to maintain readiness to blow up anything in any ocean to smithereens at a moment’s notice?

It does require continuous readiness to launch nuclear ballistic missiles from a surprise location, otherwise the “mutual” part of mutually assured destruction is less assured:

https://en.m.wikipedia.org/wiki/Submarine-launched_ballistic... https://en.m.wikipedia.org/wiki/Second_strike

Also, the US essentially controls the world’s oceans, and that comes with a whole bunch of benefits, wartime or peacetime.

I think you’ve made an honest error here, confusing the power plant of the subs with their payload. SSN’s are attack subs, not armed with nuclear SLBMs like an SSBN.

Well... yes. Maybe it shouldn't, but that decision isn't up to people actually in that branch.

Yes, at least for SSBNs -- the subs that have nuclear ballistic missiles. An "undetectable" nuclear launch platform that could be anywhere in the world [ocean-wise] at any given time is part of the "nuclear deterrent". Sure, lay waste to the continental US and all of it's farm-based missile installations; the floating, traveling, launch pad will still strike back, 24 missiles each with multiple payloads each on board. That's not including the UK's fleet.

They’re mostly reconnaissance, intelligence gathering and defensive. Occasionally might fire cruise missiles if necessary.

Helps keep the bad guys and gals from trying too much.

Sounds like a lot of enemies. I wonder how 'the good guys' ended up being hated by so many.

Where bad people means enemies of the US.

No, enemies of the western world and those who have the same values as us such as Korea, Japan, Chile, Brazil, Botswana, etc.

Clearly the US and the EU have different positions on Iran - the US considers it an enemy and imposed new sanctions, the EU haven't followed the suit.

So, no, even traditional clientele have left the US

Sure we don’t agree on everything— our agendas can diverge. The EU still gets gas from Russia, clearly we differ with them on Russia.

Exactly, you don't agree on who the enemies are and 'bad guys' mean the enemies the US, not of all the countries you lumped together.

That’s to be expected, we’re not a ‘bloc’ ala USSR and its satellites.

Except you claimed the opposite, saying that the objects of the US military's attention - 'bad guys' - are the enemies of the whole bunch of countries including the EU.

Looking at how the US tries to bully Turkey - a NATO member - into cancelling the S-400 deal with Russia, by saying the US is not going protect it despite the NATO article, you are not as different from Warsaw pact as you claim.

One the one hand, 66 total worldwide units doesn’t seem like very many compared to most other pieces of military equipment. On the other hand, the per unit cost of submarines is a staggering $2 billion to $10 billion.

For perspective, the government shutdown fight is over ~1-2 submarines worth of funding.

Given a fleet of submarines is $50B and the cost to fully instrument the entire ocean with sensors is $1B, is the price of a submarine worth it anymore?

Sensors don't attack. Sensors don't even defend themselves. They are one piece of the "kill chain", but they aren't the "kinetic" piece.

Do you necessarily need a sub to kill another sub once it's detected?

Surface navy and aviation could do the job.

We don't have adequate wartime data to know for sure one way or the other. Historically, there has only been one underwater combat engagement between submarines [1] openly acknowledged (there might be classified engagements). However, even generously accounting for all submarine lost at sea accident reports as hostile engagements doesn't yield sufficient numbers of engagements to know what would happen with today's subs between each other in open warfare.

Let's hope it stays that way indefinitely.

[1] https://nationalinterest.org/blog/the-buzz/the-true-story-th...

What do magic realists say?

[1] https://jamestown.org/program/a-smarter-battlefield-pla-conc...

The target doesn't have to be a sub. The sensors could detect a surface vessel, and the sub could be the way of attacking it.

A bomber can do it cheaper and faster.

Considering how many peoples lives were disrupted over that it is just sickening. What a bunch of bs that whole situation is/was/continues to be.