The South Korean and U.S. air forces kicked off a five-day combined air exercise, Monday, amid growing concerns of North Korea conducting its seventh nuclear test soon. According to the South Korean military, Vigilant Storm, which will run through Friday, is aimed at enhancing the operational and tactical capabilities of combined air operations and bolstering the allies' combined defense posture. The exercise involves around 240 aircraft and thousands of service members from the U.S. Marine Corps, U.S. Navy and U.S. Army as well as the two nations' air forces.