Above is a B-61 Gravity Fall Nuclear Weapon in various stages of assembly. It is configured to be dropped from the B-1B Lancer, B-2 Spirit and F-16C Falcon platforms. A new model was updated in 1997 and kicks more ass than I ever want to know about. There are currently 750 Model B61-7 weapons in the U.S.A.F. stockpile. The mission-specific 1,200-pound B61-11 "bunker buster" replaces the B53, a 8,900-pound, nine-megaton bomb that was developed as a "city buster" and was later designated as a substitute for an earth-penetrating weapon.

The B53 was deliverable only by vulnerable B-52s; in contrast, the smaller and lighter B61-11 can be delivered by the stealthier B-2A bomber, or even by F-16C fighters. The B53 was the highest-yield weapon in the U.S. arsenal. Although not a true earth-penetrating weapon, it was believed capable of taking out underground targets through brute force. When fuzed for a ground burst, a small percentage of its energy would be transmitted through ground and rock to buried installations. Even a small percentage of nine megatons is a lot of destructive power. In contrast, the B61-11 offers a variable range of yields, the highest of which is only a fraction of the B53's. But because it can pierce deeply into the earth, "ground coupling" its energy output to efficiently produce a shock wave, the B61-11 is more efficient at destroying heavily fortified underground structures, enabling it to threaten the same deep targets as the B53.

Meanwhile, the B61-11's lower yields enhance its credibility as a deterrent. The B53 was too big and too "dirty" to use. Its use would have caused a massive amount of collateral damage above ground. The new B61-7, from which the B61-11 is made, has a selectable yield ranging from 0.3 to about 340 kilotons. It was first placed in service in 1985, and super-modified in 1997. (The original B61 entered the stockpile in 1968.) The B61-7 can be fuzed for air or surface bursts, and has a hardened ground-penetrator nose system with a retarded contact-burst fuzing option. It can be dropped with or without a parachute, making it deployable from B-1B, B-2 Spirit or F-16C aircraft.