South Korea, the U.S. and Japan are conducting their first joint drills of the year off the southern coast of the peninsula this week, in what one expert called the largest-ever trilateral drills on responding to North Korean threats.

Nine ships, including South Korea’s Sejong the Great-class destroyers (KDX-III), the U.S. USS Carl Vinson aircraft carrier and Japan’s Kongo guide missile destroyer, are taking part in the three-day drills set to conclude on Wednesday, according to a statement from the ROK’s Joint Chiefs of Staff.