A bunker buster uses kinetic energy and a delayed fuse to penetrate earth or concrete and explode once it reaches its target. These weapons are typically dropped from a great height. The long, narrow profile of the bomb allows it to reach high speeds as it falls toward its target. A delay fuse prevents it from exploding on contact, only detonating once the bomb comes to a rest.
The simplest fuse in a bunker buster bomb uses a timer and a propeller situated at the rear of the bomb. As the bomb falls, the slipstream causes the propeller to turn, indicating that the bomb is still in motion. Only after the propeller has stopped moving and the timer runs out does the device detonate. More advanced bombs use sensors to detect the sound of impact and can even delay detonation until a specific number of floors in a structure have been penetrated.
In a traditional bunker buster, the kinetic energy required to breach fortifications comes from the dense construction of the bomb and its long fall from altitude. Computer-controlled fins can help steer the weapon to ensure it hits its target. For particularly hardened bunkers, the bombs may employ a rocket motor that is triggered at the last moment to provide extra thrust and kinetic energy to increase penetration.