I'm paywalled from the article but it's pretty well known that both Russian and China have subs close to, or even in, US territorial waters on a fairly regular basis.
How do you know your super-quiet sub is undetectable by the most likely adversary?
You send in the super-quiet sub on a series of probes, each time getting closer, until there's contact and possibly an incident. Now you know how good the adversary is!
Were you alive during the cold war? That's what I think this is. A kind of cold war against a terrestrial foe, in this case one with superior technology.
