The U.S. and South Korean navies kicked off anti-submarine and other maritime exercises in the East Sea on Monday, in what the ROK called a response to North Korea’s unveiling of a new “tactical nuclear attack submarine” and repeated attempts to launch spy satellites.

The joint exercises are scheduled to run for three days and involve a total of nine South Korean and U.S. warships, including ROKS Yulgok Yi-i Destroyer and USS Shoup equipped with the Aegis combat system, according to an ROK navy press release.