A DARPA-funded project has successfully developed a .50 caliber sniper round capable of maneuvering during flight in order to remain on target. The self-guiding EXACTO bullet, as it's being called, is optically guided by a laser that must remain on target for the bullet to track. The EXACTO round is capable of accurately tracking a target up to 1.2 miles away, DARPA stated. The technology, which is being developed by Teledyne Scientific and Imaging, is targeted at helping snipers remain at longer distances from targets as well as improving night shots. While DARPA's tracking bullet is the first to use a standard, small-arms caliber round, in 2012 Sandia National Laboratories (SNL) successfully demonstrated a prototype self-guided bullet that was more like like a four-inch dart.
To DARPA. We can also thank them for getting Google's driverless cars program started