US and South Korean troops will practice destroying North Korean weapons of mass destruction during an annual joint exercise this month. South Korea's Yonhap news agency today said the allies will form a combined unit called the Joint Task Force for Elimination when they begin a 10-day Ulchi Freedom Guardian exercise on August 16. Ulchi Freedom Guardian is an annual computer-assisted simulation command-post exercise. Yonhap said some 350 troops from the US Army's 20th Support Command and South Korean soldiers will simulate the detection and destruction of North Korean atomic bombs, missiles and chemical weapons. US and South Korean officials described the exercise as defensive and routine. The North habitually describes such joint drills as a rehearsal for invasion.