Ultrasound technology (SONAR), first used during World War II to detect enemy submarines, is still used to locate submersed objects. In 1998 a team of scientists, led by underwater archaeologist Robert Ballard, went in search of the USS Yorktown, an aircraft carrier that was sunk during the Battle of Midway in 1942. Using a SONAR sled and a robot, the team developed digital images of the Pacific Ocean floor; after analyzing the images, they pinpointed the remains of the ship.