Remember the Chinese sub in 2003 that was found on the surface with its entire crew dead. https://en.wikipedia.org/wiki/Chinese_submarine_361
U make my point!
Conceiving, Developing, building and operating safely and successfully the most up to date attack sub is damn near impossible for all except the US, Britain and Germany.
What’s their common denominator? Gobs of experience!!!
You could publish every plan or spec or diagram there is on one on the front page of the NYT and it all would be Greek to 99.99999999999 % of the worlds population!