U.S. Warships Get Ready for Kim Jong Un's Missiles in First Trilateral Drills since ICBM Launch

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An MK45 lightweight gun is seen on the deck of USS Stethem missile destroyer for a bilateral exercise in Singapore on July 19, 2016. The missile destroyer is now taking part in two-day missile-tracking drills with South Korea and Japan. Roslan Rahman/AFP/Getty Images

The U.S., South Korea and Japan have begun a two-day missile-tracking exercise in the waters between the Korean Peninsula and Japan in their first trilateral anti-missile drills since North Korea test-launched its most powerful rocket to date on November 29.

South Korean military said the exercise involves the three countries' Aegis destroyer warships: the Americans' guided-missile destroyers USS Stethem and USS Decatur, South Korea's Seoae Ryu Seong-ryong Aegis destroyer and Japan's Chokai Aegis ship.

South Korea and Japan will be practicing in their respective waters, each with a U.S. ship, South Korean media reported. The three countries are engaging in a computer-simulated detection and tracking of an incoming missile from North Korea, with the purpose of sharing and analyzing the data.

These are the sixth trilateral drills conducted since they were first held in June 2016. The last time they were held, in October, the U.S. sent the USS Stethem and another destroyer, the USS Milius, to join South Korean and Japanese vessels.

The Aegis naval system is one line of defense against a potential missile fired from North Korea, designed to intercept a ballistic missile before it re-enters the Earth's atmosphere. The Aegis ships are equipped with radars capable of detecting and tracking up to 100 missiles simultaneously. They can fire interceptors to take down the rockets or send data to ships closer to the missiles' flight paths. The system's ability to intercept ballistic missiles is dependent on the ships' position in relation to the missiles' targets.

The ability to share information is key to the functioning of the system. However, while the Aegis can link the data between the three countries' warships, and the U.S. system can work with either Japan or South Korea, they cannot all work together because of different data encryption systems, as Carl Schuster, a professor at Hawaii Pacific University and former director of operations at the U.S. Pacific Command's Joint Intelligence Center, told CNN.

The anti-missile training follows the U.S. and South Korea's largest-ever joint air force exercise last week, which involved American B-1B bombers participating in simulated drills, along with more than 200 other fighter jets from the two forces, in a show of strength against Pyongyang.

North Korea's Rodong Sinmun newspaper, a mouthpiece of the ruling party, condemned the Vigilant Ace drills in an article published Monday, calling the exercise part of a "war of aggression to mount a surprise pre-emptive attack" on the country.

Pyongyang has hailed the launch of the Hwasong-15 intercontinental ballistic missile as a "breakthrough" in the country's missile development program. "The day was a significant day when the historic cause of completing the state nuclear force, the cause of building a rocket power, was realized," North Korean leader Kim Jong Un said.

North Korea insists the missile does not pose a threat to anyone other than the "imperialists" of the United States, which it considers the "sworn enemy of the Korean people."