ICBMs have the distinct advantage of being able to provide a wide scale attack with high precision and short preparation/response time. This makes it a perfect deterrent.

But between the long preparation time, the chances of being discovered ahead of time, and the low relative impact/reach, even when placed strategically a few car-nukes would probably deliver more of a "terror strike" type of attack. You can cripple a few weak points but nothing "terminal".

We have had aircraft and ground stations collecting the residual isotopes of every nuclear test since the nuclear age began. We can forensically track these back to the origin reactor/enrichment facility. These facilities also "leak" so we can figure it out. If black market, we and the original source nation (unless they want to be nuked) would probably be able to track down who it went to.

Having a covert facility and deploying a weapon w/o any testing would be beyond the capacity of all but a handful of states.

If the US bombs you and rises strong check on naval traffic and frontiers it is not going to be easy. Overall missiles protect from other missiles.

What's the strategic advantage of blowing up the NYC harbour? Most probably none.

The port of New York and New Jersey is the third busiest United States port, and the busiest on the east coast. The United States economy basically lives on import and export of goods through sea freight. Bombing the NYC harbor also is an attack on US prestige in a way that bombing other harbors such as Los Angeles and Long Beach wouldn't be.

The US has a lot of busy ports, so maybe blockading one isn't too disruptive, but it still has strategic value. Of course, it also depends on the effectiveness of the bomb.

Your statement made me curious. As a percentage of GDP imports and exports constitute roughly 25%:

  https://en.wikipedia.org/wiki/List_of_countries_by_trade-to-GDP_ratio

That's the sixth lowest in the world. Only Pakistan, Argentina, Brazil, Sudan, and Nigeria have a lower ratio.

It didn't. It killed a lot of indians and firemen who got sick and created a pretext to destroy Iraq and Afghanistan (the Taliban destroyed this one first). The attack on the WTC was just stupid. It only fuelled more destruction and death, probably got Dick Cheney's pals richer, annoyed a lot of people with tightened airport security, created some extra jobs for security personnel and generally made air travel shittier for everyone.

The strategic advantage of blowing up NYC harbour is getting bombed back in time before stone tools where a thing.

That's why you'd do it in this fashion.

A nuke in a random container on a ship filled with thousands of them, owned by a bunch of shell companies, combined with the fact that the evidence gets blown up in the process...

Quite a bit harder to track to a source than "hey look a rocket launched from Iran".

Not really. It’s a fairly short list of organizations with the means and the motivation. If you’re already spying on them it’s not hard to pick up on changes in communication, movements or even catch them red handed on a recorded line.

An attack like that would also be carte blanche to nuke whoever the hell you wanted — that wasn’t themselves a nuclear power that could survive the volley — in retaliation.