The United States and South Korea will launch a major military exercise on Sunday in the Sea of Japan. The US-led United Nations Command said the four-day drill starting from 25th would involve about 20 ships including the 97,000-ton aircraft carrier USS George Washington and some 200 fixed-wing aircraft. It said 8,000 army, air force, navy and marine personnel from the two allies will take part in the exercise. US Defense Secretary Robert Gates and the South's Defence Minister Kim Tae-Young today said in a joint statement that the drill is the first in a series designed to send a clear message to North Korea that its aggressive behaviour must stop. South Korea, the United States and other nations, citing findings of a multinational investigation, accuse the North of sending a submarine to torpedo the Cheonan warship near the tense Yellow Sea border in March. The North denies involvement in the sinking, which claimed 46 lives, and says any retaliation could spark war.