The BLU-109 is a hardened penetration bomb used by Spam military aircraft. (BLU stands for Bomb Live Unit.) It is intended to smash through concrete shelters and other hardened structures before exploding. The sort of targets this beast is sent after includes secure command locations, protected weapon storage, and key transportation and communication resources all safely stashed underground.
It weighs in about 2,000 pounds (1 ton appox) and carries a 550-pound tritonal high-explosive blast warhead.
Its configuration is relatively slim. Its skin is much harder than a standard bomb casing and is a single-piece, forged warhead casing of one-inch, high-grade steel. This allows it to penetrate 6 feet of reinforced concrete. Think of it as a very large steel jacketed exploding bullet.
It has a tail fuse which is on a delay to allow penetration before exploding.
To ensure accuracy, the BLU-109/B was always mated with a laser guidance kit to form a laser-guided bomb as used extensively in Operation DESERT STORM.