The exercise, running until next Friday, brings together 7,400 soldiers to training activities which span air, land and sea as well as a jungle survival course.
6,000 US soldiers take part in the event, four times the number last year.
Cobra Gold is the biggest military exercise in the Asia-Pacific region with seven participating countries in main war exercises namely Japan, the US, Thailand, South Korea, Indonesia, Malaysia and Singapore.
Ten nations, including Vietnam will join as observers.
