Nuclear weapons delivery
Nuclear weapons delivery is the technology and systems used to place a
nuclear weapon at the position of
detonation, on or near its intended target. Several methods have been developed to carry out this task.
Weapons which are used primarily as part of a doctrine of
deterrence by threatening large targets, such as cities, are known as "strategic" nuclear weapons. These usually, but not always, have very large
explosive yield. Weapons meant for use in limited military maneuvers, such as destroying specific military, communications, or infrastructure targets, are known as "tactical" nuclear weapons, and are usually of much smaller yields. Reliance on yield to differentiate can be problematic, though, as by modern standards, the bombs that destroyed
Hiroshima and Nagasaki in
1945 may perhaps be considered tactical weapons (with yields between 13 and 22 kilotons), though they were not used in a tactical manner.''
Basic methods of delivery for nuclear weapons are discussed in the following sections.
Gravity bomb
|
The first nuclear weapons, such as the "Fat Man" device, were large and cumbersome gravity bombs. |
Historically the first method of delivery, and the method used in the two nuclear weapons actually used in warfare, is as a
gravity bomb, by a
bomber.
No nuclear weapon qualifies as a "wooden bomb" — US military slang for a bomb that is trouble-free, maintenance-free, and danger-free under all conditions. Gravity bombs are designed to be dropped from planes, which requires that the weapon can withstand vibrations and changes in air temperature and pressure during the course of a flight. Early weapons often had a removable core for safety, installed by the air crew during flight. They had to meet safety conditions, to prevent accidental detonation or dropping. A variety of types also had to have a fuse to initiate detonation. US nuclear weapons that met these criteria are designated by the letter "B" followed, without a hyphen, by the sequential number of the "
physics package" it contains. The "
B61", for example, was the primary bomb in the US arsenal for decades.
Various air-dropping techniques exist, including
toss bombing,
parachute-retarded delivery, and
laydown modes, intended to give the dropping aircraft time to escape the ensuing blast.
The first gravity nuclear bombs could only be carried by the
B-29 Superfortress. The next generation of weapons were still so big and heavy that they could only be carried by
bombers such as the
B-52 Stratofortress and
V bombers, but by the mid-
1950s smaller weapons had been developed that could be carried and deployed by
fighter-bombers.
Ballistic missile
Missiles using a
ballistic trajectory usually deliver a
warhead over the horizon. Some
ballistic missiles may have a range of tens to hundreds of kilometers, while larger
intercontinental ballistic missiles (ICBMs), including
submarine-launched ballistic missiles (SLBMs), carry out a
sub-orbital spaceflight.
Historically, the Soviet
Fractional Orbital Bombardment System was designed to carry out a partial orbital spaceflight: a
low Earth orbit, with deorbiting after less than one full orbit. The system was phased out in January
1983 in compliance with the
SALT II treaty.
An ICBM is more than 20 times as fast as a bomber and more than 10 times as fast as a fighter plane, and also flying at a much higher altitude, and therefore more difficult to defend against.
Early ballistic missiles carried a single warhead, often of
megaton-range yield. Because of the limited accuracy of the missiles, this kind of high yield was considered necessary in order to ensure a particular target's destruction.
Since the
1970s modern ballistic weapons have seen the development of far more accurate targeting technologies, particularly due to improvements in
inertial guidance systems. This set the stage for ICBMs with
multiple independently targetable reentry vehicles (MIRVs) with up to a dozen independently targetable
warheads, usually in the hundreds-of-
kilotons-range yield, on one ballistic platform. This has a number of advantages over a missile with a single warhead. Within limits it allows a single missile to strike multiple targets, or it can inflict maximum damage on a single target by attacking it with multiple warheads, making defense even more difficult than it is already, due to, among other things, the high speed. Soviet plans in the '70s were said to entail dropping one MIRV based warhead every ninety seconds to three minutes on major US targets for up to an hour.
Missile warheads in the American arsenal are indicated by the letter "W"; for example, the W61 missile warhead would have the same
physics package as the B61 gravity bomb described above, but it would have different environmental requirements, and different safety requirements since it would not be crew-tended after launch and remain atop a missile for a great length of time.
Cruise missile
|
Cruise missiles have a shorter range than ICBMs, but would be harder for an enemy to detect or intercept. |
A
cruise missile is a
jet engine or
rocket-propelled
missile that flies at low altitude using an automated guidance system (usually
inertial navigation, sometimes supplemented by either
GPS or
mid-course updates from friendly forces) to make them harder to detect or intercept. Cruise missiles can carry a nuclear warhead. They have a shorter range and smaller payloads than ballistic missiles, so their warheads are smaller and less powerful.
As opposed to conventional cruise missiles, which sometimes use
cluster munition payloads, and as opposed to bombers, nuclearly armed cruise missiles have a single warhead.
The
AGM-129 ACM (Advanced Cruise Missile) is the
US Air Force's current nuclear-armed
air-launched cruise missile. The
START II treaty forbids the USA from using stealth weapons on stealth aircraft, therefore the ACM is only carried on the
B-52 Stratofortress. This plane can carry 20 missiles. Thus the cruise missiles themselves can be compared with MIRV warheads. The
BGM/UGM-109 Tomahawk sea-launched cruise missile is capable of carrying nuclear warheads, but does not in present configurations.
Cruise missiles may also be launched from mobile launchers on the ground, and from naval ships.
There is no letter change in the US arsenal to distinguish the warheads of cruise missiles from those for ballistic missiles.
Other delivery systems
|
The Davy Crockett artillery shell was the smallest nuclear weapon developed by the USA. |
Other potential delivery methods include
artillery shells,
mines such as the
Medium Atomic Demolition Munition and the (very odd)
Blue Peacock, and nuclear
depth charges and torpedoes for
anti-submarine warfare. An atomic mortar was also tested. In the
1950s the U.S. developed small nuclear warheads for air defense use, such as the
Nike Hercules. Further developments of this concept, some with much larger warheads, showed promise as
anti-ballistic missiles. Most of the United States' nuclear air-defense weapons were out of service by the end of the
1960s, and nuclear depth bombs were taken out of service by
1990. However, the USSR (and later Russia) continues to maintain anti-ballistic missiles with nuclear warheads. Small, two-man portable tactical weapons (erroneously referred to as
suitcase bombs), such as the
Special Atomic Demolition Munition, have been developed, although the difficulty to combine sufficient yield with portability limits their military utility.
|
The Mk-17 was an early U.S. thermonuclear weapon and weighed around 21 short tons (19,000 kg). |
The key
nuclear weapon design issue related to delivery mechanisms is miniaturization— the physical size of a warhead most generally limits what kinds of delivery systems it can be coupled with. As an example, the first hydrogen bombs weighed over a dozen tons and could only be delivered by the largest of aircraft. Later thermonuclear warheads, which were engineered to fit on top of missiles, were designed to weigh around a quarter of a ton.
A second issue is accuracy. It has been suggested, for example, that Soviet nuclear weapons were designed to be of greater yield than U.S. weapons to compensate for the lesser accuracy of Soviet delivery vehicles.
Finally, there is the issue of penetration.
(See article Robust Nuclear Earth Penetrator) Nuclear weapons designed to detonate in the atmosphere often have a salvage or impact fuse that detonates them if they, unintendedly, hit the ground. The salvage fuse may even be designed to detonate when the weapon is about to be destroyed by an
anti-ballistic missile; this requires an even faster fuse. [
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*
Nuclear weapon design*
List of nuclear weapons*
Nuclear weapon yield*
Nuclear explosion*
History of nuclear weapons*
Atomic bombings of Hiroshima and Nagasaki*
Mutual assured destruction*
Nuclear warfare*
Nuclear strategy*
Nuclear missile defense
