Is it not for a bunch of little islands that Vietnam is having issues with China on?
That would be my guess. Since the Chinese have learned that they don't have anything at all to fear from Obama, maybe he thinks that a well-armed Vietnam will scare the willies out of them?
What could possibly go wrong? (Considering the Charlie Foxtrot that Obama foreign policy has been over the last 7 1/2 years -- probably a lot!)