Two of Taiwan's four submarines were launched during WWII. Both are theoretically operational, but only safe for training - and probably only safe in a shallow harbour. One is Hai Shih (ex US Tench class that was GUPPY converted). The other is Hai Bao/Pao (SS-792) (ex US Balao class also GUPPY converted) (pictured above).
Cut away of Taiwan's latest 2 submarines of the Hai Lung class, (also known as Chien Lung class) commissioned in 1987-88 (Diagram courtesy Dutch Submarines . com)
Submarine Matters' article Netherlands Needs New Submarines Quickly has led to many comments below that article regarding Taiwan's needs. This is because the Netherlands supplied Taiwan with Taiwan's most recent two subs. These were of the Hai Lung class (pictured above) supplied to Taiwan and commissioned into the Taiwanese Navy way back in 1987-88.
Taiwan has sought newer submarines for decades. This has been complicated by Taiwan's reliance on the US - which does not build suitable conventional submarines (SSKs). US backing is needed in the face of China's ability to prevent any actual conventional submarine builder from helping Taiwan.
Conventional submarine builders Germany, France, Spain, Japan and Sweden have been placed under Chinese political and economic pressure not to sell subs to Taiwan, not to help Taiwan build subs or even sell submarine components to Taiwan. The US would not allow Taiwan to buy Russian SSKs. Middle countries that have built subs under licence, like India, Australia and South Korea, have also been warned by China not to sell to Taiwan.
Chinese force aside China is a much larger and attractive a market for all products for all countries than Taiwan is. So there are many positive reasons why, for example, Germany will sell submarine engines to China and Sweden will sell AIP systems to China instead of Taiwan.
Taiwan's old anti-communist credentials are no longer considered important enough to gain sufficient cooperation from the US. This is a further complex situation where around one million Taiwanese happily trade with China or live in China. The US is also happily trading with communist Vietnam. China also underwrites or owns much of the US economy.
Some Taiwanese see a submarine project brokered by the US as a way to restore US political, military and economic support - in another sense restoring US recognition of Taiwan's right to exist.
The US especially, under the moderate Democrat Obama, is not anti-Chinese or anti-Communist enough to damage relations with China to the degree some in Taiwanese want. Taiwan may have to wait for another Republican hawk like George W. Bush (Jr) to enter office before the US might help. As the US 2016 election runup stands Hilary Clinton won't change Taiwan's sub situation and even if Republican Trump were elected, his personal business interests may well preference China over Taiwan. Are there any election eligible US Republican anti-Communists with a Presidential chance?
An additional problem is some Taiwanese want the US to broker a submarine deal in order that the US buys the subs first - in order that the US "sells' the subs to Taiwan for a highly US subsidized low price.
Another disincentive for the US is that the US Navy and submarine industry do not want to have any financial or project dealing with SSKs. For the US Navy this is because SSKs unit for unit are less capable than the US SSNs. For US industry the price/profit per SSN is much higher than for an SSK.
China's growing ASW capabilities, including China's undersea sensors and growing submarine numbers mean Taiwan will need ever more expensive, larger, more capable SSKs. If Taiwan replaced its 4 sub fleet one for one it may well need subs that are SSNs to constitute any kind of deterrent against China's rapidly growing SSN and SSK fleet.
The US won't give/sell SSNs to Taiwan. It is more reasonable that the US quietly assures Taiwan that US SSNs will defend Taiwan - to a reasonable extent.
The following are useful:
Over the years Defense Industry Daily (DID) has compiled a longer and more detailed account of Taiwan's fruitless replacement submarine efforts - particularly Taiwan’s Force Modernization: The American Side, July 21, 2015. Taiwan's submarine problems are best seen from a combined arms perspective including consideration of surface ships, naval airpower and land-based anti-shipping and anti-submarine missiles - particularly in the Taiwan Strait.
DID notes: [The Taiwanese] are even reportedly considering building their own boats from foreign designs. suggests that this course may be fraught with peril, and Taiwan has a number of technology gaps to address: ship design technology, torpedoes, sonar, propulsion systems, combat systems, and submarine periscope lenses [to which could be added submarine steel].
Meanwhile http://thediplomat.com/2015/05/taiwans-submarine-saga/ puts up a range of "US will do it" options that are not in America's economic, political or strategic interests to do.
http://news.usni.org/2015/07/08/essay-chinas-submarine-solution-for-the-taiwan-strait indicates China's skill in building a Yuan sub force that makes for major strategic problems for Taiwan and the US to counter this force
http://sputniknews.com/military/20150722/1024934686.html of July 22, 2015 describes how China is rapidly building its ASW strength - rendering Taiwan's replacement submarine efforts largely irrelevant.
Please connect with Submarine Matters Taiwan's Aging Submarine Force Limited by Mainland China of February 5, 2014 - you will notice little has changed.
So unless the US builds around 8 large SSKs in the US under a new Republican President, after 2016, Taiwan is likely to wait forever for an effective submarine force.