over the next three years. as u.s. troops draw down. five bomb attacks hit shiite pilgrims in iraq today. 21 people were killed. nearly 100 were wounded as shiites travel to karbala for important religious ritual. shiites are often targeted as they walk to and from the city since security inside the city is tight. we learn today that the u.s. drone missing and believed to be in the hands of the iranians is one of the most advanced in the american arsenal. national security correspondent is here to tell us what that means. >> good evening. u.s. military sources confirm to fox that the missing drone is rq-170 sentinel. the stealth drone went missing thursday along the western afghan border. is now believed to be in iranian hands. according to multiple u.s. officials. the drone apparently broke its tether, broke contact with its handlers.