Japan and the United States have begun their biggest ever joint military exercises, amid growing tension in the region between North and South Korea.
More than 44,000 Japanese and American military personnel are taking part in the drill off the southern islands of Japan.
Forty Japanese and 20 US warships are also involved, as are hundreds of military aircraft.
Codenamed Keen Sword, the exercises are being held to mark the 50th anniversary of the US-Japan alliance.
South Korean observers are present for the first time.
North Korea shelled the South Korean island of Yeonpyeong on 23 November, killing two marines and two civilians.
US Secretary of State Hillary Clinton said North Korea remained "an immediate threat to the region around it, particularly to South Korea and Japan".
North Korea also posed "a medium-term threat, should it collapse, to China", she said.
Beijing has criticised the manoeuvres and called for more talks with Pyongyang.