A U.S. B1-B bomber is escorted by a South Korean F-15K fighter as they fly over South Korea, during a 10-hour mission from Andersen Air Force Base, Guam, into Japanese airspace and over the Korean Peninsula on Sunday.

Hundreds of American and South Korean military aircraft began a massive drill Monday, days after North Korea test-fired an intercontinental ballistic missile it says is capable of striking the “whole” U.S. mainland.

Two dozen stealth jets from the U.S. Seventh Air Force were among the aircraft taking part in the five-day Vigilant Ace, an annual exercise in the Korean Peninsula. The exercise, which was scheduled before North Korea launched its new Hwasong-15 missile Wednesday, involves 230 aircraft and about 12,000 service members.

North Korea claims to have achieved its goal of becoming a nuclear state with the launch of the missile, which landed in the Sea of Japan.