China is preparing for a potential naval war with the US. She would be wise to gain operating experience and develop relationships with nations in that area. Indonesia/Malaya are very complex archipelagoes with multiple straits vital to world trade and transit between the Pacific and Indian Oceans. Both the USN and IJN recognized this in WWII and fought some grim battles there. It is also an area with lots of offshore oil, as well as choke points for mid-east oil for China and Japan.

That "earthquake" was a great excuse to get some ships in that area, I bet those vessels they sent are also equipped to eavesdrop on the naval communications of other countries, too. Incidentally, isn't it curious the Chinese had seismic observatories in that region?

The US Navy is also developing some littoral warfare ship designs I believe are optimized for low-intensity warfare in just this type of marine environment: lots of islands, narrow straits, confined, shallow waters, places where carriers and submersibles are at a disadvantage. Obama is very interested in the Western Pacific, as we have always been, and there has been some talk of reopening the US bases at Cam Rahn Bay and Da Nang to US warships. The Vietnamese are more afraid of the Chinese than they are of us.

This doesn't mean either power is contemplating war with the other, just that for both sides, a little pre-planning is only prudent.