“What in the world does Indonesia need with a submarine?”
To keep an eye on it’s commercial airliners...?
Ouch...LOL!
It won't matter if China gets serious - without an actively interventionist US Navy they could ultimately conquer Southeast Asia and even Australia with far less difficulty than Japan faced in 1942. They have the economic power to compel obedience, which Japan did not. Indonesia having a submarine or two might deter some illegal fishing vessels - that's about it.