US Air Force First Lieutenant Marcus Corbett of Air Force Space Command is being helped to the resting area by medical technicians after completing the grueling obstacle course during the CHIEF's Challenge portion of DEFENDER CHALLENGE 2000 at Lackland Air Force Base, Texas. Defender Challenge is the annual Air Force wide competition sponsored by Air Force Security Forces. This competition showcases the talents and capabilities of 13 international Security Forces teams in seven physical fitness, base defense and policing skills over six days