This year, South Korea is taking part in a multilateral marine exercise called Sea Dragon.
During the drills patrol aircraft from South Korea, Japan, the U.S. and Australia all train under the command of Andersen Air Force Base in Guam to capture a virtual enemy's submarine.
The drill is drawing attention as South Korea has been scaling down its joint drills with the U.S. in consideration of the denuclearization talks with North Korea.
It's also the first drill that Seoul and Tokyo are both taking part.. since their row over export restrictions and their military intel-sharing pact, GSOMIA.
Observers say the drill aims to enhance coordination among countries to tackle threats from North Korea's development of submarine-launched ballistic missiles.