It would be sufficient to destroy just the Asaluyeh gas infrastructure near the South Pars field. It's easily approached over the open sea where Iran has negligible air defences, and it is rather... flammable. It provides something like 75% of Iran's domestic gas supply and in turn fuels most of their power stations.

Their economy would implode within days.

Of course, this would be a horrific crime against humanity, comparable in impact on civilians to dropping a nuke on a capital city.

Speaking of which: my partner knows next to nothing about warfare and while watching the news I had to explain that the US Navy submarine mentioned by the presenter isn't just for taking out enemy ships, it is a nuclear-armed "world ending" weapon that could simply... erase... a country. Or two. Probably three. In under an hour.