The US Air Force successfully launched an unarmed intercontinental ballistic missile early Thursday. The Minuteman III dummy warheads were fired at 3:14 a.m. and traveled about 4,200 miles (6,758 kilometers) before hitting a water target in the Marshall Islands. The launch was delayed by a day because of a power outage at a radar facility that handles flights in and out of Southern California. The purpose is to test the defense system's reliability and accuracy. Earlier this month, North Korea shook up the world by firing several missiles into the Sea of Japan, including a failed long-range missile. The North Korean launch raised questions about the readiness of the US missile defense system, which includes interceptors housed in underground silos in California and Alaska.