Chinese aircraft can use this growing island network to criss-cross the sea in search of Western (including Australian) submarines. See Submarine Matters September 2015 article on the 3 Reefs.
Woody Island defends the approaches to China's much more important Yulin/Sanya naval base (in part a nuclear submarine base) on China's large Hainan Island. Woody also defends other Chinese naval bases and trade routes. Woody is well placed for launching strike aircraft and land attack missiles against air/naval bases on Vietnam's coast.
It is likely that China's active SSBNs consist of 4 Jin class, Type 094 submarines (4 more being built). Unlike the US, UK and France, which have a technological and development time lead in quiet SSBNs, Chinese SSBNs are believed to be significantly noisier. This means China relies on creating a safe bastion to defend its growing SSBN, SSN and SSK forces. Without this "bastion" China's SSBNs cannot amount to a credible second strike capability because they would be destroyed too quickly (particularly by the US SSNs operating out of Guam).
A principal role of China's SSNs and SSKs is defending its SSBNs from Western (US) SSNs and (Japanese, Australian, South Korean and perhaps Singaporean) SSKs.
The bastion defences are in the form of:
- long range DF-21D anti-shipping/anti-submarine missiles based on the Chinese mainland and maybe Hainan.
- Hainan, Woody and 3 Reefs based MPAs, helicopters and ASW warships
- Large Chinese ASW UAVs (eg. "Divine Eagles") are also being developed which will be launched from the island/reefs.
- For ASW and anti-shipping China can also string its undersea SeaWeb (SOSUS just part of it) networks between the island/reefs and the Chinese mainland. These networks can be laced with seabed or tethered mines, which can be remote-armed against Western shipping and subs during times of crisis.
China's conventional diesel-electric submarines (SSKs) only have limited range and endurance. Woody Island and the 3 Reefs provide much needed friendly-to-China bases where the SSKs can refuel and replenish other supplies (including specialised AIP chemicals for the Yuan class SSKs).
China's increasing militarisation of the Paracels (including Woody) means that Australia needs submarines of increasingly longer range. Australia's future subs need to be able to operate from Fleet Base West (south of Perth) - quickly transit to-from (more than 6,000 kms total) and actually remain on station for around 4 weeks unrefueled.
Chinese satellites and long loitering UAVs will soon mean that Australian submarines cannot transit/operate surfaced at any stage. Operating the diesels while running across Chinese SeaWeb networks will also become dangerous. Lithium-ion batteries and AIP may become essential - on the way to nuclear propulsion (within the next 25 years).