The two-day exercise took place in the Sea of Japan and involved four warships: the Japanese JDS Chokai guided missile destroyer, the South Korean DDG Seoae Ryu Seong-ryong destroyer, and the American USS Stethem and Decatur guided missile destroyers.
All of them were equipped with the Aegis ballistic missile defense system. The American-made missile defense system is meant to detect, track and shoot down incoming missiles. "During the drill, Aegis warships from each country will simulate detecting and tracking down potential ballistic missiles from the North and sharing information," the South Korean Defense Ministry wrote.
This is the sixth trilateral drill between the three nations since June 2016.
The drill comes after a Pyongyang test of their new intercontinental ballistic missile (ICBM), the Hwasong-15, in late November. While the test failed due to the missile's faulty re-entry mechanism, the Hwasong-15 was shown to have nearly global reach. North Korea declared that they had officially achieved nuclear statehood, sending peninsula tensions skyrocketing.
Shortly after the Hwasong-15 test, the US and South Korea began their largest ever joint air drill, Vigilant Ace. The exercises involved 230 aircraft, including F-22 and F-35 stealth fighters and B-1B strategic bombers that can be equipped with nuclear payloads. Nearly 12,000 American soldiers participated in the drills over the unfriendly skies of the Korean Peninsula.
While Vigilant Ace is an annual exercise that had been announced long in advance, it brought criticism of the US from Moscow and Beijing. The US' fellows on the UN Security Council chastised the Americans for continuing a cycle of provocation with Pyongyang.
"The situation is in a vicious cycle of provocation and confrontation. This is not conducive to regional peace and stability," Chinese Foreign Ministry spokesman Lu Kang said during a press conference. "If such a vicious cycle continues and leads to a very bad result, it serves no party's interest."
South Korean President Moon Jae-in has traveled to Beijing for a summit with Chinese President Xi Jinping, meant to smooth over relations. Although overshadowed by the broader problem of North Korea's missile program, China has been vocally displeased with South Korea's deployment of the American-made Terminal High Altitude Area Defense (THAAD) earlier in 2017 and the general strengthening of military ties between Seoul and Washington.
Meanwhile, Gen. Valery Gerasimov, chief of the General Staff of the Russian military, met with Japanese Defense Minister Itsunori Onodera in Tokyo and called on the Japanese government to push for a peaceful resolution to the crisis.
"We believe that this issue should only be resolved through political and diplomatic means," Gerasimov said, according to a statement from the Russian Defense Ministry. He criticized Japanese participation in military exercises as threatening to "destabilize the situation."
Onodera replied that "North Korea's nuclear and missile development are significant threats against the international community. I want us to cooperate over this problem."
China is North Korea's dominant trade partner, accounting for over three quarters of all their foreign trade. Russia is a distant second. Both nations have agreed to UN sanctions levied against North Korea as retaliation for the expansion of their nuclear missile program.