Nuclear weapons delivery is the technology and systems used to place a nuclear weapon at the position of detonation, on or near its target. Several methods have been developed to carry out this task.
Strategic nuclear weapons are used primarily as part of a doctrine of deterrence by threatening large targets, such as cities. Weapons meant for use in limited military maneuvers, such as destroying specific military, communications, or infrastructure targets, are known as tactical nuclear weapons. In terms of explosive yields, nowadays the former have much larger yield than the latter, even though it is not a rule. The bombs that destroyed Hiroshima and Nagasaki in 1945 (with TNT equivalents between 15 and 22 kilotons) were weaker than many of today’s tactical weapons, yet they achieved the desired effect when used strategically.
Main delivery mechanisms
Historically, the first method of delivery, and the method used in the only two nuclear weapons actually used in warfare, was a gravity bomb dropped by a plane. In the years leading up to the development and deployment of nuclear-armed missiles, nuclear bombs represented the most practical means of nuclear weapons delivery; even today, and especially with the decommissioning of nuclear missiles, aerial bombing remains the primary means of offensive nuclear weapons delivery, and the majority of US nuclear warheads are represented in bombs, although some are in the form of missiles.
Gravity bombs are designed to be dropped from planes, which requires that the weapon be able to withstand vibrations and changes in air temperature and pressure during the course of a flight. Early weapons often had a removable core for safety, known as in flight insertion (IFI) cores, being inserted or assembled 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 earliest gravity nuclear bombs (Little Boy and Fat Man) of the United States could only be carried, during the era of their creation, by the special Silverplate limited production (65 airframes by 1947) version of 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 six/ten-engined, seventy-meter wingspan B-36 Peacemaker, the eight jet-engined B-52 Stratofortress, and jet-powered British RAF V bombers, but by the mid-1950s smaller weapons had been developed that could be carried and deployed by fighter-bombers.
Missiles using a ballistic trajectory usually deliver a warhead over the horizon, at distances of thousands of kilometers, as in the case of intercontinental ballistic missiles (ICBMs) and submarine-launched ballistic missiles (SLBMs). Most ballistic missiles exit the Earth’s atmosphere and re-enter it in their sub-orbital spaceflight.
Placement of nuclear missiles on the low Earth orbit has been banned by the Outer Space Treaty as early as 1967. Also, the eventual Soviet Fractional Orbital Bombardment System (FOBS) that served a similar purpose—it was just deliberately designed to deorbit before completing a full circle—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. ICBMs can also be fired quickly in the event of a surprise attack.
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 smaller warheads in the hundreds-of-kilotons-range yield, and consequently for ICBMs having multiple independently targetable reentry vehicles (MIRV). Advances in technology have enabled a single missile to launch a payload containing several warheads. The number of independent warheads capable of deployment from ballistic missiles depends on the weapons platform the missile is launched from. For example, one D5 Trident missile carried by an Ohio-class submarine is capable of launching eight independent warheads, while a Typhoon has missiles capable of deploying 10 warheads at a time.
MIRV has a number of advantages over a missile with a single warhead. With small additional costs, it allows a single missile to strike multiple targets, or to inflict maximum damage on a single target by attacking it with multiple warheads. It makes anti-ballistic missile defense even more difficult, and even less economically viable, than before.
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.
Other delivery methods included artillery shells, mines such as the Medium Atomic Demolition Munition and the novel Blue Peacock, nuclear depth charges, and nuclear torpedoes. An ‘Atomic Bazooka’ was also fielded, designed to be used against large formations of tanks.
In the 1950s the US developed small nuclear warheads for air defense use, such as the Nike Hercules. From the 1950s to the 1980s, the United States and Canada fielded a low-yield nuclear armed air-to-air rocket, the AIR-2 Genie. Further developments of this concept, some with much larger warheads, led to the early anti-ballistic missiles. The United States have largely taken nuclear air-defense weapons out of service with the fall of the Soviet Union in the early 1990s. Russia updated its nuclear armed Soviet era anti-ballistic missile (ABM) system, known as the A-135 anti-ballistic missile system in 1995. It is believed that the, in development (2013) successor to the nuclear A-135, the A-235 Samolet-M will dispense with nuclear interception warheads and instead rely on a conventional hit-to-kill capability to destroy its target.
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.
Hypersonic Glide Vehicles are a new potential method of nuclear delivery. They can be potentially combined with ICBM MIRVs such as RS-28 Sarmat.