In a landing exercise on Wednesday, amphibious armored vehicles advanced toward the shore from the sea under cover of a smoke screen. Once they reached shore, South Korean soldiers with firearms disembarked and assumed their positions.
The US military used air-cushioned landing craft to ferry armored vehicles ashore, while Osprey aircraft and helicopters flew in formation to transport soldiers inland.
The South Korean military says the exercise involved about 30 vessels and 70 aircraft.
Both countries are making it clear they intend to firm stance against North Korea, which has been accelerating its nuclear and missile development.
US Carrier joins the joint exercise
The US sent a nuclear-powered aircraft carrier to participate in the drills.
The USS Nimitz joined an exercise off the South Korean island of Jeju on Monday.
Fighter jet pilots rehearsed their takeoff and landing maneuvers, while naval personnel confirmed and reviewed protocols for guarding the carrier.
Rear Adm. Christopher Sweeney, commander of Carrier Strike Group 11, said, "I feel pretty confident in our capability to operate in the sea in any given time and in any place."
After the drill, the USS Nimitz docked in the South Korean port city of Busan on Tuesday morning.
After the carrier leaves port, it will take part in a trilateral exercise with the Japan Maritime Self-Defense Force and the South Korean Navy.
South Korea's Yonhap News Agency says the carrier is likely to leave port early next week.
North Korea reacts sharply
North Korea appeared to respond to the drills by firing missiles.
Tuesday's edition of the ruling Workers' Party newspaper, Rodong Sinmun, said a missile unit fired the ground-to-ground ballistic missiles from Pyongyang.
South Korea's military has said the North launched two short-range ballistic missiles from near Pyongyang on Monday morning.
The Rodong Sinmun also said the country completed a three-day test of an "underwater nuclear attack drone" on Monday. It said the "Haeil-1" set off from Wonsan in the east on Saturday and cruised along a course simulating a distance of more than 600 kilometers.
North Korea has also unveiled what appear to be tactical nuclear warheads.
State-run Korean Central Television said Tuesday that Kim was briefed the day before by the Nuclear Weapons Institute on new nuclear arms development and the country's "nuclear weapon combined management system."
The broadcast said Kim examined plans and written orders for nuclear counterattack operations. He also reportedly issued a directive to expand the production of weapons-grade nuclear materials and spur the manufacture of more powerful nuclear weapons.