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.