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Weapons of war

Man holding an AK47

Why are there laws about weapons?

In a word, humanity. Wars are dreadful, causing death and injury to very large numbers of people. But if there were no banned weapons, the death and injury – and therefore the suffering – would be much, much worse. So there are international agreements which ban some types of weapons entirely, and limit the use of others.

What is the basis for banning the use of some weapons?

It is helpful to think of three central ideas. One is that weapons should not be indiscriminate. Another is that weapons should not cause unnecessary suffering or superfluous injury. The third is that the use of weapons in war should be guided by principles of "distinction, proportionality and military necessity". All that sounds quite technical. The explanations below should help to make it clearer.

What is meant by indiscriminate weapons?

If, by their nature, weapons cannot be directed at a specific target, or if their effects cannot be controlled, they are considered to be indiscriminate. So, for example, a booby-trap weapon, designed to look like a harmless object, but which can kill or injure when someone approaches, cannot be controlled. It is indiscriminate.

Similarly, one of the reasons that anti-personnel landmines have been banned is that they cannot distinguish between civilians and soldiers.

What weapons cause unnecessary suffering or superfluous injury?

Ones that go beyond what is strictly necessary to achieve a military aim. For instance, it is widely accepted that once someone has been shot by a bullet, they tend not to take any further part in hostilities. So there is no further advantage in a bullet that explodes on impact. Such weapons were invented as long ago as the nineteenth century, and they make injuries much worse. But they don't bring any real military advantage to the side that fired them. So, on humanitarian grounds, exploding bullets are banned.

Another explicit ban is on weapons which injure by fragments that are not detectable in the human body by X-ray. They are prohibited because they achieve nothing, other than prolonging suffering and preventing treatment.

What are the principles of distinction, proportionality and military necessity?

In a conflict there are combatants and military targets. There are also likely to be civilians and civilian objects. Distinction is all about identifying and respecting the very important difference between the two. Civilians should be protected against military operations. They should not be targeted for attack. The use of weapons in ways that do not preserve that difference is likely to be illegal.

Note that this does not mean that civilian deaths are always a result of a violation of the law. Those in charge of forces – both politicians and military leaders – must take constant care to spare the civilian population. They cannot target civilians directly, and must "take all feasible precautions" in the way they attack, to avoid or minimise incidental loss of civilian life, injury to civilians, and damage to civilian objects.

It follows that if an army acts to achieve its military objectives, and keeps civilian casualties to a minimum, it can be acting lawfully. The guiding principle is known as proportionality – meaning that the loss of civilian life or damage to civilian property must be proportional to the military advantage anticipated.

Likewise, it does not follow that using weapons to attack civilian structures – such as roads, bridges or television stations – is necessarily illegal. If such objects, at the time of attack, also serve a military purpose then attacks may be acceptable in law, always bearing in mind the requirement of proportionality.

Is there a fixed list of banned weapons?

Not exactly. A few weapons are banned entirely, such as anti-personnel landmines. More are subject to limits – such as the restrictions on the use of booby-traps. But providing a list would be difficult, as weapons are constantly being developed. Instead the law has to look at basic principles and apply them.

But also, as the previous discussions show, the way weapons are used can be as important as what they actually do. For example, incendiary weapons – ones that are primarily designed to spread fire or to burn – are prohibited in all circumstances against civilians. But lawful use against soldiers is possible. Some weapons may be lawful for use against buildings or enemy tanks but not if directed at troops.

Could the use of nuclear weapons be legal?

It is an undecided question. On one hand, the civilian deaths and injury would be so enormous that the use of nuclear weapons would be "contrary to the principles and rules of international humanitarian law", as the International Court of Justice has put it. On the other, if a state was acting in self-defence, and its existence threatened, it could be argued that a use of a nuclear weapon was the best and necessary way of defeating the enemy. Experts disagree. At the moment there is no prohibition on nuclear weapons.

What is the difference between biological and chemical weapons?

They are sometimes bracketed together because they are different from the guns, explosives, rockets and missiles that are known as conventional weapons. Chemical weapons work, crudely, as poisons. They have toxins that cause death or incapacitation on contact with humans. They include mustard gas and nerve agents and other chemicals that can asphyxiate or irritate and blister skin.

Biological weapons act on the human life system and are often developed from living organisms such as viruses or bacteria. They are greatly feared because relatively small amounts, for example of deadly spores carrying anthrax, can cause immense numbers of casualties. That's why, along with nuclear weapons, they are often thought of as "weapons of mass destruction".

Are there circumstances where biological and chemical weapons are permitted?

No. The use of biological and chemical weapons is prohibited. Countries, including the UK, which had experimented with such weapons development have closed their programmes. If any such development is happening anywhere in the world, it takes place secretly.

The ban on chemical and biological weapons is so absolute that it does not matter whether they are lethal or not, or whether they are allowed by domestic laws. For example, CS gas can be used by police to control riot situations. But its use is prohibited in armed conflict.

Where is the law about weapons written and how is it enforced?

What soldiers call the "laws of armed conflict" is also known as international humanitarian law, particularly in humanitarian and legal circles. The main treaties are the Geneva Conventions of 1949, developed by later agreements known as Additional Protocols. However, the main laws about weapons are contained in separate conventions, equally legally binding, on specific types of weapon. These include the 1972 Biological Weapons Convention, the 1980 Conventional Weapons Convention and the 1997 Ottawa Convention on anti-personnel landmines.

Alleged breaches of the law can be tried in national courts, or by the International Criminal Court at the Hague. It is a sad fact that there are many breaches. War is extremely violent and very many desperate and appalling things happen. But those breaches don't undermine the need for the laws, or for improved compliance.

Have the laws on weapons made a difference?

Almost certainly, though it is very hard to quantify. It can also be hard to appreciate when media reports are full of graphic stories of death and injury. It is worth remembering that news media focus on disturbing and exceptional cases. Those occasions when armies take care to avoid injury to civilians are simply not reported – partly because few people know about them, and partly because "no civilians injured" does not make a news headline.


Activities and discussion

  • There is an outright ban on laser weapons designed to cause permanent blindness to enemy soldiers. Discuss this ban. What is students' reaction to the idea of deliberately causing blindness to large numbers of people? It strikes many people as barbaric. Is this just an emotional reaction? Why are blinding laser weapons regarded as different from weapons that kill?
  • In reality, the judgements about military necessity and proportionality in war have to be made by commanders on the ground. Some take their responsibilities very seriously – and even check with the International Committee of the Red Cross for clarification. Yet there are breaches, which are only rarely the subject of legal action. Talk about why this is. Would the world be a better place if investigations automatically took place after conflicts into soldiers' and politicians' behaviour? How practical does it seem? What are the arguments for and against?
  • Nuclear weapons are characterised by their destructive power, the unspeakable suffering caused by their use, the fact that it is extremely difficult to bring aid to victims, the fact that it is impossible to control their effects in space and time, the risk of escalation and proliferation which any use of nuclear weapons necessarily involves, and the dangers which such weapons entail for the environment, future generations and the survival of humanity. So says the International Committee of the Red Cross. It is calling on governments to reach an agreement to ban these weapons. Do students agree?



This briefing was written by PJ White.

This resource and other free educational materials are available at


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