A massive joint amphibious exercise involving the navy and marines of South Korea and the U.S. has kicked off amid a series of missile launches by North Korea.

According to the South Korean military, the 2023 “Ssangyong” training exercise began in Pohang, North Gyeongsang Province on Monday and will run through April 3, the first iteration of the drill in five years with the scale of participating units expanded from brigades to divisions.

The Ssangyong drill is a part of the ongoing spring joint exercise, Freedom Shield, covering its outdoor maneuver and field training sessions.

Over 30 vessels are taking part in the Ssangyong drill, including South Korea’s ROKS Dokdo amphibious assault ship and the USS Makin Island, a U.S. Wasp-class amphibious assault ship.

Also mobilized are some 70 aircraft, including F-35B stealth jets and AH-64 Apache attack helicopters as well as 50 amphibious assault vehicles.