China is having issues with their subs being loud, so is NK and likely Iran (if they even have any nuke boats).
Knowing how the reactor works also lets them figure out what sort of noise profile it makes, so they can hunt our stuff easier.
This cpuple wasn't selling the keys to Fort Knox, but they could definitely get subs sunk that didn't have to be.
Actually, submarine tech is probably the most sensitive of all government secrets, so, yes they actually WERE effectively giving away the keys. And the article says that it wasn’t just reactor related information.
At a minimum, I’d say probably France, Israel, Brazil, or Turkey. *Possibly* India, Taiwan, South Korea or Japan, but I think those are much less likely. The first because India is also occasionally cozy with Russia and is as much of an ally of convenience as a friend; the second because 1) I don’t think they’re interested in an SSN program at this time beyond spitballing 2) Pissing off the Americans right now in particular would be suicide, and 3) If it wound up in China’s hands -and the ROC is pretty heavily penetrated- it’d be even more dire; the latter two because while they’re pursuing SSN programs, using stolen American data would have very nasty consequences if they were found out.
France is iffy because they aren’t above that sort of thing, but even with the hissy fit they threw over AUKUS, it’s almost certain to result in an even more severe backlash if they fucked around. Israel is more land and air power; their navy is basically for coastal defense. Brazil I think has some interest, and I know Argentina definitely has expressed interest in an SSN program, but they both (Argentina more so) would be in massive deep shit with the U.S. Both are Major Non-NATO Allies (so they get all sorts of goodies and such that most countries can’t), and fucking around with the crown jewels of American military secrets is a sure fire way to get it revoked.
Incidentally, keep in mind that for all the U.S. and Britain already share stuff, we and they DON’T share submarine info beyond certain things like Trident. The British keep their sonar and surveillance gear to themselves, and we do much the same with our reactor tech and other stuff.