I've long been a supporter of Taiwan having submarines. Strategypage covers the latest in Taiwan's efforts to build their own.
Taiwan needs subs to threaten an invasion flotilla and to pose a threat to Chinese sea trade. Taiwan has just two aging boats plus two antique training boats.
Basically, foreign submarine builders don't want to risk China's ire by selling subs to Taiwan.
America doesn't build conventional subs and it would cost too much to get American sub builders set up to build conventional subs.
In the past I read that our Navy lobbied against building conventional subs out of fear that Congress would try to save money by building cheaper--but shorter legged boats that is a crucial deficiency given the distance our subs have to go--conventional subs for our Navy. This does not invalidate the actual cost discovery issue, of course.
Yet while nobody wants to risk China's anger and retaliation by selling subs to China, many are willing to sell components, which will help Taiwan build their own. And American sub suppliers can sell a lot of components useful for conventional as well as nuclear subs.
So if Taiwan is willing to pay the price, Taiwan can build their own. And upgrades to an ancient World War II model used for training only will be good experience for building new boats.
And Taiwan is running out of time as their two useful boats get old. Without a replacement (and Taiwan wants 8 boats, in theory), Taiwanese sailors aren't eager to pin a career on this uncertain path and morale is low in their sub service.
So China has incentive to throw sand in the gears to slow down Taiwanese progress. How far will China go to do this? Will pressure on suppliers, propaganda, pressure on sympathetic Taiwanese legislators, and espionage be supplemented by direct action (theft; destruction of property; blackmail, bribery, murder, and kidnapping of key personnel) to sabotage research and production?
Because the payoff of such action is potentially high. Significant delays in the program could push integration of subs into Taiwan's fleet past either an invasion by China or past the survival of Taiwan's submarine operating institutional knowledge if too many sailors leave the navy and younger sailors don't choose subs as their career path.