Is the US GBU-57 MOP a lawful weapon? An Article 36 analysis.

While the Israel's 'Operation Rising Lion' against the Iran's uranium enrichment capability enters its second week, global attention turns to whether the US President will authorise the use of the GBU-57 Massive Ordnance Penetrator (MOP), a bunker-busting bomb, to strike the deeply buried facility.

Following the International Atomic Energy Agency's (IAEA) recent report acknowledging that the Islamic Republic of Iran was enriching uranium to a higher level than other countries without nuclear weapons programs, the Israeli government ordered a series of military strikes against Iran's nuclear weapons capability including its military commanders, nuclear facilities and even nuclear scientists. Israel claimed in its letter to the United Nations Security Council that the attacks were in self-defence against the existential threat of an imminent nuclear attack by Iran against Israel.

While the legality of the Israel Defence Force (IDF), and potentially US, strikes againt Iran under international law is the subject of debate the focus has turned to the concern that Iran has build its uranium enrichment facility deep inside a mountain bunker in Fordow, northeast of Qom. Moreover, that the depth of the underground facility protects it from the conventional weapons within Isreal's military arsenal and that the only weapon capable of attacking a facility at this depth is the US GBU-57 MOP. This weapon is more than 13 tonnes and is significantly larger than other bunker busting munitions.

Why is the GBU-57 unique?

The GBU-57 is an earth penetrating weapon designed to attack targets deep underground by using its substantial weight and speed to penetrate before exploding. Its penetrating effect is aided by a dense alloy nose casing designed to survive deep penetration before detonating the nearly 2.5 tonnes of explosives. The GBU-57 utilises GPS and inertial navigation systems to provide it with the ability to strike within meters of its intended target. It is claimed that the GBU-57 can penetrate up to 60 meters before exploding.

Is the GBU-57 lawful?

All States are required by international law to determine the legality of its weapons before their use in armed conflict. While the US is not a State Party to the Additional Protocol I to the Geneva Conventions of 1949 (AP I)(and therefore not bound by the Article 36 legal review obligation) they nontheless have a long standing legal review process as a matter of national policy.

As the GBU-57 was developed by the US Air Force it falls to the USAF Judge Advocate General Corps (JAG) to conduct legal reviews of its weapons under a Secretary of the Air Force Directive. The legal review is designed to ensure a weapons legality under US domestic and international law. The JAGs conduct their legal review analysis on the basis of a weapon's normal or expected use in light of international weapons law treaties binding the US and customary international law.

How does international regulate weapons?

International weapons law is primarily created through multi-lateral treaties binding only upon State Parties however many treaty based prohibitions are recoginsed a reflecting customary international law and therefore binding on all states. International law also prohibits weapons which cause certain prohibited effects including:

a. superfluous injury or unnecessary suffering to combatants,

b. indiscriminate effects i.e. the weapon cannot be aimed at a specific military target, and

c. weapons that cause long term, wide spread and severe harm to the natural environment.

International weapons law regulates the legality of weapons in two ways: first the legality of the weapons itself (weapons law); and secondly the legality of the use of the weapon in armed conflict (targeting law). A legal review primarily determination primarily focusses on weapons law and therefore the legality of any attack on the Iran uraniunium enrichment facility is dealt with separately to the weapon review process.

There is no international law specifically prohibiting the GBU-57 MOP as a class of weapon. Despite the massive size of the bomb, international law has not determined that such a weapon is unlawful and, in reality, international weapons law prohibitions generally follows international concern resulting from the misuse of a weapon in armed conflict. Equally, in the absence of humanitarian controversy, States are reluctant to seek international law prohibitions or restrictions against weapons with ongoing military utility.

While there are no specific international law prohibitions, there are relevant questions as to weather the GBU-57 causes indiscriminate effects and if it causes long term, wide spread and severe harm to the natural environment.

A weapon is unlawful 'per se' where it is indiscriminate by nature and therefore cannot be aimed at a specific military objective. The GBU-57 is a modular weapon which includes the bomb itself and then a GPS/inertial guidance system that work in conjunction with stabalising grid fins to allow mid-flight directional adjustments. GBU stands for 'Guided Bomb Unit' and it is this capacbility that is relevant. It is claimed that the GBU-57 is capable of reliably striking within meters of its intended target. If this is accurate the GBU-57 is discriminate and therefore not prohibited on the basis that it causes indiscriminate effects.

However, the other relevant aspect to the rule against indiscriminate effects is the prohibition in Article 51(4) of AP I which prohibits attacks, 'which employ a method or means of combat the effects of which cannot be limited as required by this Protocol' and 'consequently, in each such case, are of a nature to strike military objectives and civilians and civilian objects without distinction'. The risk that the attack on the Iranian nuclear facility may release nuclear material in a way that cannot be controlled is a valid targeting law question however it is not determinate of the legality of the GBU-57 itself as it is not designed to cause such an effect.

Next, is the question of environmental harm. Article 35(3) of AP I states that, 'It is prohibited to employ methods or means of warfare which are intended, or may be expected, to cause widespread, long-term and severe damage to the natural environment.' It is important to note that the US is not a party to AP I and therefore are not bound by this rule and it is not clear whether the US regard this rule to be a norm of customary international law and therefore binding.

The long-term nature of the damage referred to in art 35(3) is generally measured in decades and, therefore, would not include environmental damage caused by conventional warfare, such as from the explosive effects of artillery barrages. We would need to understand more about the likely effect of the GBU-57 underground explosion to make an accurate determination of this issue.

It is likely that a US legal review of the GBU-57 would determine it to be a lawful weapon per se. The more critical legal questions concern the legality of the use of force in self-defence by Isreal and potentially the US and whether the specific attack against the Iranian nuclear facility is lawful. Both of these questions however fall outside the scope of the legal review of the weapon itself.

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