Nuclear weapons use the physics of ‘fissile materials’1 to create a very

large explosion. The smallest possible nuclear explosion is similar in size to

some of the largest possible conventional (ie non-nuclear) explosions,2 but

most nuclear weapons involve explosions many thousands or even millions

of times larger than that.3 As with any large explosion, the heat and blast

effects kill and injure people, topple buildings and cause other widespread

destruction. Unlike any other type of explosion, however, nuclear weapons

also release radiation, which is uniquely harmful to humans in a range of

different ways (see chapter 2).


The early ‘atom bomb’ was based on nuclear fission – splitting the

atoms of uranium or plutonium in a chain reaction that rapidly creates

temperatures hotter than the interior of the sun. At those massively high

temperatures, other elements can also break apart to ‘boost’ the fission

process and atoms of hydrogen can fuse together to create helium, causing

an even larger explosion. This is where the term ‘hydrogen bomb’ came

from, although the latter process is called nuclear fusion.


Today, most nuclear weapons incorporate all three stages into a single

weapon: a fission bomb is detonated first, to create the temperatures needed

for fusion, a neutron ‘booster’ then multiplies the impact of the fission

process, and finally a fusion bomb is exploded, using hydrogen to create

the maximum blast for the minimum quantity of fissile material.


When we talk about nuclear weapons we are mainly talking about the

nuclear warhead, where the explosion takes place. To be used as a weapon,

the warhead must be made into a free-fall bomb or put onto a missile so it

can reach its target. Bombs and missiles also require some form of platform,

or ‘delivery vehicle’, to launch the weapon. Delivery vehicles include aircraft,

submarines, missile silos, mobile missile launchers and other delivery systems.

Nuclear weapons have been produced in all shapes and sizes since 1945.


The smallest nuclear weapons ever deployed had a destructive capacity

equivalent to around 10 tonnes of tnt, or 0.01 Kilotons (0.01 kt). The largest

nuclear weapons ever deployed were in the 20–25 mt (25,000 kt) range.

Most nuclear weapons today are between 100–1,000 kt (or 0.1 – 1 mt)

in size.


Nuclear weapons capable of reaching targets many thousands of miles

away are considered ‘strategic’ weapons. These are delivered by long-range

bomber aircraft, ballistic missile submarines or inter-continental ballistic

missiles (icbms). Nuclear weapons with a shorter range, measured in hundreds

rather than thousands of miles, are considered ‘intermediate’ nuclear forces,

and normally these are defined in terms of the shorter range of bomber

aircraft or missiles.


Nuclear weapons with a very short range, measured in miles or tens of

miles, are considered ‘battlefield’ or tactical nuclear weapons. During the

Cold War, tens of thousands of battlefield nuclear weapons were facing

each other in Central Europe. These included nuclear weapons fired from

artillery pieces, dropped from helicopters, fired from trucks and jeeps,

dropped as depth charges from ships, fired from torpedo tubes and even

nuclear weapons designed to be carried into battle strapped onto the backs

of soldiers and then detonated from a distance.

Who has nuclear weapons?

As of mid-2017, only nine states are producing and deploying their own

nuclear weapons: The United States, Russia, China, uk, France, India,

Pakistan, Israel and North Korea. South Africa developed and tested a nuclear

weapon but then gave up its nuclear programme. Eleven other countries

toyed with the idea of developing their own nuclear weapons and gave up

their programmes before actually testing a nuclear device.4 At least 37 other

countries are considered economically and technically capable of producing

nuclear weapons if they chose to do so.


According to the us Bureau of Arms Control, Verification and Compliance,

reporting in April 2017 under the terms of the NewSTART Treaty,5 the us

currently has a total of 1,411 deployed nuclear warheads on 673 delivery

vehicles and Russia has 1,765 deployed nuclear warheads on 523 delivery

vehicles. These numbers do not include nuclear warheads which are considered

‘stockpiled’ or ‘retired’. Both countries have approximately 4,000 warheads

in the first category and 2,500 in the second category, bringing the total

warhead count up to around 7,000 nuclear warheads each.6


The uk claims to have 120 warheads operationally deployed on its

Trident submarines, with another 95 ‘stockpiled’, for a total of 215. France

and China both have close to 300 warheads in total. France is considered

to have nearly all its warheads ‘deployed’ while China is not considered to

disarming the nuclear argument: the truth about nuclear weapons

have any of its warheads deployed.7 India and Pakistan currently have

between 100–150 each, although again these are not considered to be

deployed. Israel is believed to have around 80 nuclear warheads and North

Korea around eight.


That makes for a grand total of just under 15,000 nuclear warheads in

the world as of early 2017, of which around 4,000 are ‘operationally

deployed’. Many of these are, in turn, on hair-trigger alert, ready to be fired

at a moment’s notice.


At the height of the Cold War in the mid-1980s, there were more than

60,000 nuclear warheads in the world. More than 45,000 nuclear warheads

have been successfully taken out of service and dismantled since then, meaning

a reduction by three-quarters in the total number of nuclear weapons.

Virtually all of the largest nuclear weapons in the multi-megaton range

have been removed since the height of the Cold War. Ironically, perhaps, so

have most of the smallest nuclear weapons in the 1–10 Kiloton range and

smaller. Currently, the smallest nuclear warhead in the us arsenal is in the

50 Kiloton range and the largest is in the 455 Kiloton range. While it is

difficult to know for sure, the largest nuclear weapon currently deployed by

Russia is probably in the 1,000 Kiloton range (1 mt) and the smallest is

probably in the 10 Kiloton range.


The uk has only one type of warhead, and that is believed to be in the

100 Kiloton range, although they have at times claimed to also have a smaller

yield option. All of France’s nuclear warheads are now in the 150–300 kt

range, while China is believed to still have nuclear weapons in the 3,000–

4,000 kt (3–4 mt) range, as well as weapons as small as 20 kt.

The impact of a nuclear detonation

The Hiroshima bomb was estimated to be in the range of 12,000–18,000

tonnes of tnt (12–18 kt), or roughly 1,000 times as powerful as the largest

conventional bomb in the us arsenal today.8 The total number killed by

the Hiroshima bomb is not known. The original estimate of 68,000 dead

and a similar number injured was based on a random survey of households

in 1946. However this did not take into account up to 20,000 Korean

prisoners of war and an unknown number of refugees from other Japanese

cities known to be in the city at that time.


Many of those who were injured by the Hiroshima blast died subsequently

from radiation sickness and fatal injuries, in part because medical facilities

were destroyed and very little was known about the dangers of radiation

poisoning. It is difficult to know how many of the subsequent deaths in

Hiroshima should be attributed to the atomic bomb as opposed to other

causes. Most sources now use the figure of 140,000 as the total number

killed by the Hiroshima bomb, although the city of Hiroshima maintains an

official register of deaths from the atomic bomb right up to the present day,

and that register now has more than 200,000 names.9


The atom bomb which was dropped on Nagasaki was of a different

design and estimated to be slightly more powerful at 20 kt. The total death

count was initially estimated at 60,000, or slightly less than at Hiroshima.

A much larger number were injured but more of these people survived than

in Hiroshima. Other differences between the death tolls in the two cities had

to do with weather conditions, terrain, the type of buildings, the population

density of the city and where the bomb was dropped in relation to where

people were at the time.


A modern nuclear warhead with a yield of 100 kt is 6.6 times the size

of the Hiroshima bomb. The scale of the destruction and the number of

people who would be killed or injured from such an explosion is difficult

to determine and depends on many factors, including those just mentioned

above. There is not a linear relationship between the size of a nuclear

explosion and the numbers killed or area destroyed. The biggest factor has

to do with whether the bomb is detonated at, or near, the ground or higher

up in the atmosphere (see next chapter). Nevertheless, based on what we

know about Hiroshima, it is clear that the effects of a single nuclear weapon

today, detonated on, or above a city, would be devastating.


The nuclear fireball

The detonation of a nuclear weapon creates a massive fireball as the nuclear

chain reaction, or ‘fission’, breaks down the atoms of uranium and/or

plutonium that are the initial fuel of the bomb. The temperature inside this

fireball rises to tens of millions of degrees Centigrade. This is hotter than

the interior of the sun and thousands of times hotter than a conventional

explosion.10 Inside the fireball, these temperatures trigger the thermonuclear

‘fusion’ reaction that creates even more destructive energy as atoms of

hydrogen are fused into helium and other by-products. The fireball of a

100 kt warhead is a sphere approximately 500 metres (1,500 ft) across in

all directions.


If the fireball is 500 metres across and the centre of it is more than 250

metres above the ground, this is called an ‘airburst’. With the whole of the

fireball in the air, very little else is consumed by the fireball other than the

nuclear fuels contained in the bomb and small quantities of oxygen and

other gases in the air. If the fireball is detonated below this height, this is

considered a ‘groundburst’. Everything within that sphere is then turned

into radioactive by-products as a result of the explosion, and this is a critical

factor which we shall explore in greater detail in the next chapter.


From a basic airburst explosion, already more than 300 different radioactive

isotopes are created from the exploding uranium and/or plutonium.11

Many more varieties of radioactive material may be additionally created from

a groundburst explosion, depending on what was on the ground at that

precise time and place. If the target of a groundburst explosion was a nuclear

missile silo, nuclear weapons store or other nuclear facility, any nuclear

warheads or other nuclear materials – as well as living creatures – that end

up within reach of the fireball are themselves going to be irradiated and added

to the total fireball and subsequent release of radioactive by-products.


Heat and blast effects

Conventional explosives cause death, injuries and destruction of property

from the heat and blast of the explosion. This rips through buildings, sets fire

to anything that burns and throws shrapnel, bits of building and other debris

through the air, all of which is highly dangerous to anything or anybody that

may be nearby. A nuclear explosion causes all these same effects, in addition

to the unique effects of radiation, which are discussed in the next chapter.


At a distance of 4 km from a 100 kt nuclear explosion, temperatures

are still hot enough to set papers and other flammable materials alight.12

Therefore fires are an enormous hazard in the aftermath of a nuclear

explosion even at great distances from ground zero. In Hiroshima, the

entire city centre was burnt to the ground and many of the injuries suffered

by the inhabitants were the result of burns.


Blast is normally measured in pounds per square inch (psi) of ‘overpressure.’

13 Ten psi of overpressure is enough to damage lungs and cause

widespread fatalities and 20 psi is enough to pull down a heavily reinforced

concrete building.14 Near the nuclear fireball, the shock wave which is

created by the explosion reaches 200 psi of overpressure, with winds of more

than 2,000 mph, enough to flatten and kill anything, even the most heavily

reinforced concrete bunker.15 At 1 km (0.6 miles) from a 100 kt blast, the

overpressure is 20 psi, which is lethal for human beings and still capable of

considerable damage to buildings. At 2 km, the overpressure still reaches

5 psi, with windspeeds over 100 mph and up to 50 per cent fatalities.16


Nuclear winter and nuclear famine

Another product of a nuclear explosion is the dust and soot that rises up as

a result of fires and the intense heat created. Most atmospheric tests took

place on Pacific islands, barren atolls or in the deserts of western us, central

Australia or Siberia. Under these conditions, even groundburst explosions

would not be expected to cause major fires and therefore the soot content

has been minimal. If a nuclear explosion took place over dense forest or a

densely populated city, however, fires could be expected to burn out of

control for some days over a large area. This happened in Hiroshima and

Nagasaki as well as in places like Dresden and Tokyo where conventional

explosives were used in huge quantities to create ‘firestorms’.


During the 1980s there was concern that an all-out nuclear war between

the Soviet Union and the West could push so much soot into the atmosphere

that it would lead to a ‘nuclear winter’ – a lowering of global temperatures,

causing widespread famine, disease and death of large numbers of people

not already killed by the nuclear weapons themselves or the after-effects of



The us and Russia each had an estimated 2,500 mt worth of tnt in

their nuclear arsenals at that time and climate scientists calculated that an

all-out nuclear war would therefore put about 150 million tonnes of soot

into the atmosphere. Using complex computer modelling of the earth’s

climate, they estimated that that much soot could lower the earth’s average

temperature by as much as 8.5 degrees C and reduce annual rainfall globally

by as much as 1.4 mm. This in turn would reduce growing seasons worldwide

and mean that some key grain-producing regions like Iowa and Ukraine

would remain below freezing even in the height of summer and thus unable

to grow anything for up to two years.17


Using the same modelling techniques, scientists then tried in the 1990s to

estimate the climatic effects of just 100 Hiroshima-sized bombs, for instance

in a regional war between India and Pakistan.


Given the population densities in those two countries and the vulnerability

of crops to radiation damage, it was concluded that even a ‘small-scale’

nuclear war in that region would have hugely devastating consequences

for all the countries across the whole Northern Hemisphere and could lead

to the death of over two billion people.18


Further studies have looked at the effects of ‘limited’ forms of nuclear

warfare, for instance the launching of nuclear weapons from a single uk

Trident submarine. Dr Philip Webber, chair of Scientists for Global

Responsibility, has estimated that the simultaneous detonation of 4 megatonnes

of tnt, roughly the total firepower of one uk Trident submarine,

could produce between 10 and 38 million tonnes of soot, sufficient to cause

a cooling of the earth by 1.5–3 degrees C and a shortening of growing

seasons by 10–30 days over a five-year period.19


How this might affect global food supplies is hard to estimate, but the

implications are clear. Even a comparatively ‘limited’ nuclear war could

cause devastating and long-lasting climactic effects, while a major all-out

nuclear war would endanger the entire planet.


Targeting nuclear weapons

At the end of wwii, the us was the only country with nuclear weapons.

Although there was talk of getting rid of them at that point, the us began to

rapidly build up its arsenal of nuclear weapons as well as the means to

deliver them. By 1946, the us had a total of nine atomic bombs, but had

already identified a list of 20 major cities in the Soviet Union to drop them

on. By 1948, the us had about 50 nuclear weapons. Their targeting plans

at that point still involved dropping them on those same 20 cities, only by

this time they would be hit by at least two nuclear weapons each.


By 1950, the Soviet Union had acquired about five nuclear weapons of

its own. The us by this time had about 300, and their target list began to

expand very rapidly. In addition to cities, the us military began to focus on

targets that would ‘blunt, retard and disrupt’ the Soviet Union’s nuclear

weapons capability. This meant targeting industrial infrastructure, such as

chemical factories, power plants and shipyards.


By 1955, the us had over 5,500 targets in the Soviet Union, Eastern

Europe and China assigned to its arsenal of about 2,500 nuclear warheads.

And by 1960, the target list was growing exponentially as the us nuclear

stockpile increased to over 20,000 nuclear warheads. The us target list was

so large at this point it was incorporated into a ‘Bombing Encyclopedia’

which eventually listed over 80,000 targets to be hit in case of nuclear war

with the Soviet Union and/or China.


During the 1960s, there was so much ‘overkill’ built into the us nuclear

war planning that Moscow, for instance, was expected to be hit with 23

separate multi-megaton nuclear weapons. Kaliningrad would be hit with 18

nuclear weapons and Leningrad with four. Recently de-classified documents

from this period show that the us military expected the death toll in the

event of war with the Soviet Union to be in the region of 285 million dead

across the Soviet bloc, with up to 40 million injured.


During the 1970s and ’80s, us nuclear targeting plans were reviewed and

revised a number of times. The specific targeting of cities (‘counter-value’

targeting) became more controversial, not least because it became illegal under

international law following the signing of the Additional Protocols to the

Geneva Convention in 1977 (see chapter 12). However the specific targeting

of the other side’s nuclear weapons (‘counter-force’ targeting) was also highly

controversial, since it increased the risk of one side launching a first strike.


If one side can destroy the other side’s nuclear weapons in a surprise first

strike attack, that other side is under great pressure to fire their weapons

before they are destroyed. This increases the likelihood that either side will

try to be the first to launch a surprise attack, but it also increases the pressure

to ‘launch on warning’, ie to launch nuclear weapons at the very first indication

that an attack is underway, rather than waiting to verify the attack. Waiting

for confirmation that an attack is underway might mean it is too late to fire

back with weapons that have already been destroyed.


We now know from the historical record that faulty radars, technical

glitches and human error led either the us or the Soviets to believe an attack

was underway at least 11 times in the last 50 years (see Chapter 13). Only

luck saved the world from all-out nuclear war on those 11 occasions. With

‘launch on warning’ the world might not be so lucky.


Nuclear weapons are capable of causing death and destruction on a scale

unparalleled in human history. A single 100 kt nuclear warhead can produce

temperatures of tens of millions of degrees Centigrade and a shock wave

sufficient to flatten skyscrapers, together with everything else that may be

standing, or alive, within 500 metres of the blast.


At a distance of 2 km, the blast is still sufficient to bring down buildings

and cause many casualties, with wind speeds at over 100mph. At a distance

of 4 km from an exploding 100 kt warhead, the heat is still intense enough

to set newspapers on fire.


The us and Russia each have more than 1,500 warheads many times this

size, ready to launch if given the order, 24 hours a day, 365 days a year.

Altogether, there are nearly 15,000 nuclear weapons in the world today.

Launching just one of these warheads, by accident or by design, would

cause a humanitarian catastrophe of unparalleled proportions. Launching

a handful of them could push millions of tons of soot into the atmosphere

and seriously affect global food supplies for billions of people, on top of all

the other destructive effects of those weapons. An all-out nuclear war

between the us and Russia would almost certainly mean the end of modern

civilisation as we know it, and could well lead to mass global extinctions,

including of our own species.


All of this is a risk we face with weapons whose destructive power is out

of all proportion to any cause we could possibly have for their use. And yet,

we have not even taken into account the most serious by-product of nuclear

weapons – the radiation effects.