The Guided Bomb Unit-28 (GBU-28) is a special weapon developed for penetrating hardened Iraqi command centers located deep underground. The GBU-28 is a 5,000-pound laser-guided conventional munition that uses a 4,400-pound penetrating warhead. The bomb's guidance package was a GBU-24/B Paveway III GCU with software modifications to handle its different aerodynamics.
To save time, practically all parts of the bomb, originally designated GBU-28/B, were modified off-the-shelf components. The body of the BLU-113/B warhead was made of surplus U.S. Army M201 howitzer gun barrels, the nose cone and the explosive was from the BLU-109/B, and the WGU-36/B guidance package was a GBU-24/B Paveway III GCU with software modifications to handle the different aerodynamics of the bomb.