The GBU-39 Small Diameter Bomb (SDB) is a 250 lb (110 kg) precision-guided glide bomb that is intended to provide aircraft with the ability to carry a higher number of more accurate bombs.
Most US Air Force aircraft will be able to carry (using the BRU-61/A rack) a pack of four SDBs in place of a single 2,000 lb (907 kg) bomb. The small size of the bomb allows a single strike aircraft to carry more of the munitions than is possible using currently available bomb units. – United States Armed Forces
Featured image of Staff Sgt. Randy Broome signals a jammer operator to move a Bomb Rack Unit 61 forward, while loading it onto an F-15E Strike Eagle at Royal Air Force Lakenheath, England. U.S. Air Force photo/Master Sgt. Lance Cheung.