1)
The sea way to middle east, africa (gas + oil) and australia - crossing the south-chinese sea and the indic ocean - are going more and more important for china.
In economic view its very important, to save these routes in a conflict - and so the best PLAN-ships should be there to escort chinese tankers, frighters and other trading ships in case of conflicts;
2)
The SSF is operating in the biggest area - between Mainland and Singapore, Vietnam and the Philiipinas, which includes some "controversal islands" (Spratley),
East- and Northfleet could be observed by Taiwan, Japan and SK very easy, the SSF-Neighbours like the Philippinas or Vietnam didn't have these possibilitys;
thats the best place for undetected trainee-operations:
so I think the PLAN could test carrier-operations there very easy - and undetected;
3)
In a conflict with taiwan, the taiwanese islands there - Itu Aba and Tungsha Tao - would see the first demonstrations of PLANs amphibious capactiy,
so it make much sense to concentrate the amphibious fleet in the SSF (the S. Sea Fleet can quickly be deployed to assist the E. Sea Fleet in a Taiwan scenario or the N. Sea Fleet in a Diaoyutai Islands scenario.)
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About 051 C - my 5 cents - they will be part of CBG very soon;
a modern DDG without helo is ... hm, let me say, underdeveloped ...
the 051 C's have no hangar to transport and maintain helos, and they only don_t need hangar-space, if other ships could transport these helos (KA-31 AEW
which would be excellent for air-defence missile guided destroyers
source:
and KA-28 ASW) - and did anyone here know a better helo-transport-ship as a carrier?