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The map above indicates China's PLA-N, from its Eastern and Southern Theater commands, has a combined 32 SSKs available to wage a hidden blockade of Taiwan. Smart mines, UUVs and undersea sensors would act as force multipliers in this blockade.
Gabriel Honrada for Asia Times, has written an excellent article, dated August 16, 2022, which brings together many interesting points about Taiwan and Submarines.
Issues include:
China deploying some of its Yuanand Song-class SSKs for a part submarine blockade of Taiwan. This may starve out Taiwan’s economy in weeks as food, minerals, energy and other supplies that come by sea are cut. In terms of energy imports Taiwan has only a “11-day supply of natural gas and 146 days’ worth of oil”.
Use of submarines [and missiles] could minimize the need for more vulnerable Chinese surface ships and aircraft to attack in the initial phase. In terms of typical Chinese official secrecy and media management any destruction of Chinese subs is easy to conceal.
My own thoughts are Taiwanese and other Western ASW surface ships would be vulnerable to Chinese anti-ship ballistic and cruise missiles. Against Taiwanese-Western ASW and other aircraft China has HQ-9 SAMs with a range of 300km. China's S-400 SAMs have an even longer 400km range. Outside air supply of Taiwan might be deterred by the threat of Chinese SAMs.
Hidden US SSNs, Japanese and maybe South Korean SSKs are the main threat to Chinese submarines.
Australian submarines are based simply too far away to assist. Instead, Australia, as an ever loyal US ally, might feel compelled to send 2 frigates/destroyers with a supply ship. The latter ship’s cruising speed of around 15 knots would make for a slow moving flotilla – vulnerable to Chinese torpedoes and missiles. These Aussie ships may turn out to be the first Western ships China sinks.