Helicopters prepare to land in Rayong, Thailand.

These units are practicing emergency evacuations in the largest annual military drill in Asia.

The operation, called Cobra Gold, is part of a U.S. strategy to improve relations in the region.

(SOUNDBITE) (English) U.S. MARINE GENERAL CRAIG CRENSHAW

"Last year, we conducted an exercise of this sort and this year we made it a little larger. Again, this is important for all the right reasons. The opportunity for us to meet each country, how they conduct evacuation procedures and to learn from each other. So this is a great opportunity and we look forward to continue training of this sort."

Soldiers participated in the same exercise last year just before Japan's earthquake and tsunami disaster struck on March 11.

Japanese commanders say the drills are about being prepared for the worst by boosting international cooperation.

(SOUNDBITE) (Japanese) COLONEL RYOJI TAKEMOTO FROM JAPANESE ARMY

"When the Great East Japan Earthquake happened last March, Japan and the United States' cooperation in 'Operation Tomodachi' was displayed and that cooperation produced a large number of accomplishments. In order to further build multi-national cooperation, I believe this sort of training is useful."

More than 13,000 military personnel from seven countries are taking part in the exercises.

Jessica Gray, Reuters