Hillary's visit aims at showing strong support for South Korea following sinking of a South Korean warship ROKS Cheonan in Mar 26, 2010.
An international team of investigators in May 2010 found that a North Korean submarine fired a torpedo that sank Cheonan. The US and South Korea called the sinking a violation of the armistice that ended the fighting in 1953.
Hillary and Gates will hold 'two plus two' talks with South Korean counterparts.
On Tuesday, Jul 20, Gates and his South Korean counterpart Kim Tae-Young announced major joint naval exercises starting Sunday, Jul 25 as a deterrent to the North Korea.