Three U.S. nuclear-powered strike groups joined South Korean forces on Sunday to begin joint naval exercises in the East Sea in an unprecedented show of force against North Korea, a Korean military source said.

Among the three aircraft carriers, USS Ronald Reagan (CVN 76), USS Nimitz (CVN 68) and USS Theodore Roosevelt (CVN 71), one entered the operational area, called the Korea Theater of Operations (KTO) on Saturday, while the others joined later on Sunday following drills with Japan.

The KTO refers to open-sea area that the commander of the South Korea-U.S. combined forces is to zone off for military operations in case of a contingency..

The exercise comes after South Korea and the U.S. agreed in their recent defense ministers` talks to expand the rotational deployment of U.S. strategic military assets to the peninsula and has been timed with President Donald Trump’s five-country Asia tour, which centered on the North Korean issue.

It marks the first time for three U.S. aircraft carriers to be deployed for a joint exercise with South Korea, and the first time three American aircraft carriers have trained together since 2007, officials said.

During the operation that will last until Tuesday, the carriers will conduct several training activities, including precision strikes on North Korea’s nuclear and missile facilities.

A South Korean source said the allied forces in the massive joint military drill will underscore the strong might and will of the South Korea-U.S. alliance and show off their readiness to retaliate in the event of a contingency.

By Ahn Doo-won and Minu Kim

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