U.S. to conduct exercise with Vietnam

The U.S. announced today that American warships will be conducting a military exercise in the South China Sea with Vietnam, signalling closer ties with the former adversary.  China has responded with scathing remarks, claiming the U.S. has no business being in its waters, and now claims ALL of the China Sea, including disputed islands claimed by several ASEAN trade member nations.  Also announced by the U.S. Government is proposed sharing of nuclear technology, materials and assistance to Vietnam in the near future.  Vietnam claims a desire to keep China from expansionist agendas and to keep Chinese ambitions for the region in check.  What's your opinion?