This file photo shows US President Barack Obama greeting Australian troops and US Marines at RAAF Base Darwin in Darwin, November 2011. More US Marines are set to arrive in Australia's tropical north ... more 

This file photo shows US President Barack Obama greeting Australian troops and US Marines at RAAF Base Darwin in Darwin, November 2011. More US Marines are set to arrive in Australia's tropical north next month as Washington increases its military presence as part of a renewed emphasis on the Asia-Pacific less