or...
that may not be immediately identifiable.
If Russia sold subs to China.China sold them to pakistan.
Pakistan sold them to Iran... or a north african ally of theirs...
and if that nation sold or donated them to a crew of pakistan trained al quaida... and three or four crews had one or two low yield, low tech nukes that they could deliver from some distance out...
who would we nuke.
Or would we make speeches while we waited, weeks, months or even a year to 'make sure'?
'who can we nuke for nuking us?'
just a rhetorical question.
You don't think we'd notice them training.
I'm sure it would take an extensive amount of training before a bunch of landlocked middle ages warriors could even hope to pull off a highly sophisticated and epeensive operation.
What port would they train out of that we don't monitor in some way?
Where would they maintain it? Dock it? Fuel it? Etc.
A one time use would still need extensive training which would be detected somehow.