The BLU-109 is an American 2,000-pound penetrating bomb designed to destroy bridges, fortified structures, and bunkers. The bomb is capable of penetrating two meters of reinforced concrete before detonating. Despite having less explosive than a similar "simple" 2,000-pound MK84 bomb (238 kg versus 438 kg), the BLU-109 is unique in that it has a significantly thicker steel casing, as well as a special detonator that is activated a certain time after impact with the ground. All this makes underground structures like Nasrallah's bunker an ideal target for this bomb.