A U.S. Marine helicopter made a "hard landing" on Tuesday during a training exercise in South Korea, near the North Korean border.
South Korea's Yonhap news agency reports that the incident with the CH-53 Super Stallion helicopter occurred at a military shooting range in Cherwon.
According to NBC news, all 21 service members aboard were admitted to the hospital. However, 15 have already been released.
United States Forces Korea detailed in a statement that the crew was part of the 31st Marine Expeditionary Unit, stationed in Okinawa, Japan.
Safety is a priority for all aircraft operations. The CH-53E has an excellent operational safety record. A comprehensive investigation will take place to determine the facts and circumstances surrounding this incident. Safety is our number one priority when operating our aircraft, to include both the safety of our aircrew, passengers and the communities where we train and operate.
According to AFP, the U.S. has 28,500 service members permanently stationed in South Korea.
The maneuver that resulted in the "hard landing" came at the end of Foal Eagle, an annual joint military drill between the U.S and South Korea. According to the Associated Press, this year's exercises were one of the largest military maneuvers in the world.