James Dwyer, University of Tasmania

Late on Saturday night, local time, the United States carried out strikes against Iranian nuclear enrichment sites at Fordow, Natanz and Isfahan, marking its open participation in the conflict between Iran and Israel.

The US says it fired 30 submarine-launched missiles at the sites in Natanz and Isfahan, as well as dropping more than a dozen “bunker buster” bombs at Fordow and Natanz.

The kind of bomb in question is the extremely destructive GBU-57 Massive Ordance Penetrator, or MOP, which weighs around 13.5 tonnes.

The attacks raise a lot of questions. What are these enormous bombs? Why did the US feel it had to get involved in the conflict? And, going forward, what does it mean for Iran’s nuclear ambitions?

What are ‘bunker busters’, and why are they used?

Bunker busters are weapons designed to destroy heavily protected facilities such as bunkers deep underground, beyond the reach of normal bombs.

Bunker busters are designed to bury themselves into the ground before detonating. This allows more of the explosive force to penetrate into the ground, rather than travelling through the air or across the surface.

Iran’s nuclear enrichment sites at Fordow, Natanz and Isfahan are built deep underground. Estimates suggest that Fordow for example could be 80m beneath the surface, and capped with layers of reinforced concrete and soil.

What is the MOP?

The bunker buster used in this particular operation is the largest in the US arsenal. Leaving aside nuclear weapons, the MOP is the largest known bunker buster in the world.

Weighing some 13.5 tonnes, the MOP is believed to be able to penetrate up to 60 metres below ground in the right conditions. It is not known how many the US possesses, but the numbers are thought to be small (perhaps 20 or so in total).

We also don’t know exactly how many were used in Iran, though some reports say it was 14. However, it is likely to be a significant portion of the US MOP arsenal.

Why does only the US possess this capability?

The US is not the only state with bunker-busting weaponry. However, the size of MOP means it requires very specialised bombers to carry and drop it.

Only the B2 stealth bomber is currently able to deploy the MOP. Each B2 can carry at most two MOPs at a time. Around seven of America’s 19 operational B2s were used in the Iran operation.

There has been some consideration whether large transport aircraft such as the C-130 Hercules could be modified to carry and drop the MOP from its rear cargo doors. While this would allow other countries (including Israel) to deploy the MOP, it is for now purely hypothetical.

Why has the US (apparently) used them in Iran

The Trump administration claims Iran may be only a few weeks from possessing a nuclear weapon, and that it needed to act now to destroy Iranian nuclear enrichment sites. This claim is notably at odds with published assessments from the US intelligence community.

However, Israel lacks bunker-busting weaponry sufficient to damage the deeply buried and fortified enrichment sites at Fordow, Natanz and Isfahan.

Only the MOP could do the job (short of using nuclear weapons). Even then, multiple MOPs would have been required to ensure sufficient damage to the underground facilities.

The US has claimed that these sites have been utterly destroyed. We cannot conclusively say whether this is true.

Iran may also have other, undeclared nuclear sites elsewhere in the country.

Iran’s reaction

The US has reportedly reached out to Iran via diplomatic channels to emphasise that this attack was a one-off, not part of a larger project of regime change. It is hard to say what will happen in the next few weeks.

Iran may retaliate with large strikes against Israel or against US forces in the region. It could also interrupt shipping in the Strait of Hormuz, which would affect a large portion of global oil shipments, with profound economic implications.

Alternatively, Iran could capitulate and take steps to demonstrate it is ending its nuclear program. However, capitulation would not necessarily mean the end of Iran’s nuclear ambitions.

The value of nuclear weapons

Perhaps a greater concern is that the attack will reinforce Iran’s desire to go nuclear. Without nuclear weapons, Iran was unable to threaten the US enough to deter today’s attack.

Iran may take lessons from the fate of other states. Ukraine (in)famously surrendered its stockpile of former Soviet nuclear weapons in the early 1990s. Russia has since felt emboldened to annex Crimea in 2014 and launch an ongoing invasion in 2022. Other potential nuclear states, such as Iraq and Gadaffi’s regime in Libya, also suffered from military intervention.

By contrast, North Korea successfully tested its first nuclear weapon in 2006. Since then there has been no serious consideration of military intervention in North Korea.

Iran may yet have the ability to produce useful amounts of weapons-grade uranium. It may now aim to buy itself time to assemble a relatively small nuclear device, similar in scale to the bombs used in Hiroshima and Nagasaki.

Depending on what facilities and resources have survived the US strikes, the attack has likely reinforced that the only way the Iranian regime can guarantee its survival is to possess nuclear weapons.

James Dwyer, Lecturer, School of Social Sciences, University of Tasmania

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Jane McAdam, UNSW Sydney; Regina Jefferies, UNSW Sydney, and Thomas Mulder, UNSW Sydney

As thousands of Australian citizens and permanent residents stuck in Iran and Israel continue to register for repatriation flights, the government is scrambling to find safe ways to evacuate them.

With the airspace over both countries closed, the government is considering other ways to bring them home.

The current plan is to charter buses from private companies to take people from Israel into neighbouring Jordan. As Prime Minister Anthony Albanese stressed: “We want to make sure people are looked after, but they need to be looked after safely as well”.

This is not the first time Australia has faced challenges in evacuating nationals stranded abroad. When conflict, disasters or other emergencies occur overseas, the government regularly works to bring Australians home.

In the early days of the COVID pandemic, for instance, the government arranged repatriation flights and established quarantine facilities to assist Australians who were stuck outside the country. Australia has repeatedly assisted its citizens caught in conflict zones to get back home, including from Afghanistan in 2021 and Lebanon in 2024.

And when an earthquake devasted Vanuatu last December, Australia moved swiftly to get Australians out.

Is Australia legally required to repatriate people?

While there is a longstanding and widespread practice of governments repatriating their nationals in emergencies, countries generally do not have a legal responsibility to do so.

Instead, governments’ decisions are discretionary and made on a case-by-case basis. They are often influenced by diplomatic, logistical and security considerations.

Governments have a right – but not a duty – to provide consular assistance to their nationals abroad. This includes issuing travel documents, liaising with local authorities and, in exceptional cases, facilitating evacuations.

The Consular Services Charter outlines what Australians abroad can expect from their government. It makes clear that while the government will do what it can, there are limits. Assistance is not guaranteed, especially in areas where Australia has no diplomatic presence or where security conditions make intervention too dangerous.

The Department of Foreign Affairs and Trade (DFAT) is the lead agency responsible for coordinating Australians’ evacuation with embassies, airlines and international partners. Decisions to evacuate are ultimately made by the minister for foreign affairs following a recommendation, where possible, by the Inter-Departmental Emergency Task Force (IDETF).

Repatriation efforts are guided by the Australian Government Plan for the Reception of Australian Citizens and Approved Foreign Nationals Evacuated from Overseas (AUSRECEPLAN). This arrangement that sets out a process for “the safe repatriation of Australians, their immediate dependants, permanent residents and approved foreign nationals (evacuees) following an Australian government-led evacuation in response to an overseas disaster or adverse security situation”. It outlines how federal, state and territory agencies coordinate to receive and support evacuees once they arrive in Australia, ensuring that returns are not only swift, but also safe and orderly.

Challenges and constraints

Repatriation during a crisis is a complex undertaking. Quite aside from the emergency conditions, which may close off usual travel options or routes, the Australian government cannot force another country to allow an evacuation. It also cannot guarantee safe passage, especially in conflicts.

Identifying and communicating with citizens overseas can also be tricky, often requiring people to have self-registered with consular authorities to receive updates. In addition, consular services may be strained when embassies and consular offices have closed, as is the case in Israel and Iran.

For these reasons, countries sometimes band together to assist each other. For instance, Australia and Canada have agreed that where one has a consular presence but the other does not, they will help to repatriate the other’s citizens.

Similarly, the United States helped evacuate Australians and other allies’ nationals from Afghanistan after the Taliban takeover in 2021. Countries in the European Union can activate a special regional mechanism to facilitate the repatriation of their citizens caught up in emergencies abroad.

In exceptional circumstances, countries have sometimes extracted their stranded nationals through military operations, known as “non-combatant evacuation operations” (NEOs). This involves the military temporarily occupying a location on foreign soil to evacuate people. Some recent examples include the large-scale evacuations of foreign nationals from Afghanistan in 2021, Sudan during the civil war that began in 2023 and Lebanon during the 2024 Israeli–Hezbollah conflict.

NEOs generally require the consent of the country from where the evacuation takes place, but their precise legal basis remains ambiguous under international law.

In all cases, the evacuation of nationals is operationally complex – as exemplified by the current situation in Iran and Israel. Countries with limited resources may struggle to repatriate their nationals at all. This can mean some foreign nationals are “rescued”, while others are left behind.

And, of course, local populations generally aren’t eligible for evacuation at all. This can leave people in extremely dangerous circumstances.

That is why we have proposed the creation of an Australian framework for humanitarian emergencies that, among other things, would facilitate the safe and swift departure of certain non-citizens at particular risk. This would underscore that Australia’s approach to evacuations is, at its heart, about protecting people during crises.

Jane McAdam, Scientia Professor and ARC Laureate Fellow, Kaldor Centre for International Refugee Law, UNSW Sydney; Regina Jefferies, Laureate Postdoctoral Fellow, ARC Laureate Evacuations Research Hub, UNSW Sydney, and Thomas Mulder, Laureate Postdoctoral Fellow, ARC Laureate Evacuations Research Hub, UNSW Sydney

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Amin Saikal, Victoria University

Israeli Prime Minister Benjamin Netanyahu has gone beyond his initial aim of destroying Iran’s ability to produce nuclear weapons. He has called on the Iranian people to rise up against their dictatorial Islamic regime and ostensibly transform Iran along the lines of Israeli interests.

United States President Donald Trump is now weighing possible military action in support of Netanyahu’s goal and asked for Iran’s total surrender.

If the US does get involved, it wouldn’t be the first time it’s tried to instigate regime change by military means in the Middle East. The US invaded Iraq in 2003 and backed a NATO operation in Libya in 2011, toppling the regimes of Saddam Hussein and Muammar Gaddafi, respectively.

In both cases, the interventions backfired, causing long-term instability in both countries and in the broader region.

Could the same thing happen in Iran if the regime is overthrown?

As I describe in my book, Iran Rising: The Survival and Future of the Islamic Republic, Iran is a pluralist society with a complex history of rival groups trying to assert their authority. A democratic transition would be difficult to achieve.

The overthrow of the shah

The Iranian Islamic regime assumed power in the wake of the pro-democracy popular uprising of 1978–79, which toppled Mohammad Reza Shah Pahlavi’s pro-Western monarchy.

Until this moment, Iran had a long history of monarchical rule dating back 2,500 years. Mohammad Reza, the last shah, was the head of the Pahlavi dynasty, which came to power in 1925.

In 1953, the shah was forced into exile under the radical nationalist and reformist impulse of the democratically elected Prime Minister Mohammad Mosaddegh. He was shortly returned to his throne through a CIA-orchestrated coup.

Despite all his nationalist, pro-Western, modernising efforts, the shah could not shake off the indignity of having been re-throned with the help of a foreign power.

The revolution against him 25 years later was spearheaded by pro-democracy elements. But it was made up of many groups, including liberalists, communists and Islamists, with no uniting leader.

The Shia clerical group (ruhaniyat), led by the Shah’s religious and political opponent, Ayatollah Ruhollah Khomeini, proved to be best organised and capable of providing leadership to the revolution. Khomeini had been in exile from the early 1960s (at first in Iraq and later in France), yet he and his followers held considerable sway over the population, especially in traditional rural areas.

When US President Jimmy Carter’s administration found it could no longer support the shah, he left the country and went into exile in January 1979. This enabled Khomeini to return to Iran to a tumultuous welcome.

Birth of the Islamic Republic

In the wake of the uprising, Khomeini and his supporters, including the current supreme leader Ayatollah Ali Khamenei, abolished the monarchy and transformed Iran to a cleric-dominated Islamic Republic, with anti-US and anti-Israel postures. He ruled the country according to his unique vision of Islam.

Khomeini denounced the US as a “Great Satan” and Israel as an illegal usurper of the Palestinian lands – Jerusalem, in particular. He also declared a foreign policy of “neither east, nor west” but pro-Islamic, and called for the spread of the Iranian revolution in the region.

Khomeini not only changed Iran, but also challenged the US as the dominant force in shaping the regional order. And the US lost one of the most important pillars of its influence in the oil-rich and strategically important Persian Gulf region.

Fear of hostile American or Israeli (or combined) actions against the Islamic Republic became the focus of Iran’s domestic and foreign policy behaviour.

A new supreme leader takes power

Khomeini died in 1989. His successor, Ayatollah Ali Khamenei, has ruled Iran largely in the same jihadi (combative) and ijtihadi (pragmatic) ways, steering the country through many domestic and foreign policy challenges.

Khamenei fortified the regime with an emphasis on self-sufficiency, a stronger defence capability and a tilt towards the east – Russia and China – to counter the US and its allies. He has stood firm in opposition to the US and its allies – Israel, in particular. And he has shown flexibility when necessary to ensure the survival and continuity of the regime.

Khamenei wields enormous constitutional power and spiritual authority.

He has presided over the building of many rule-enforcing instruments of state power, including the expansion of the Islamic Revolutionary Guard Corps and its paramilitary wing, the Basij, revolutionary committees, and Shia religious networks.

The Shia concept of martyrdom and loyalty to Iran as a continuous sovereign country for centuries goes to the heart of his actions, as well as his followers.

Khamenei and his rule enforcers, along with an elected president and National Assembly, are fully cognisant that if the regime goes down, they will face the same fate. As such, they cannot be expected to hoist the white flag and surrender to Israel and the US easily.

However, in the event of the regime falling under the weight of a combined internal uprising and external pressure, it raises the question: what is the alternative?

The return of the shah?

Many Iranians are discontented with the regime, but there is no organised opposition under a nationally unifying leader.

The son of the former shah, the crown prince Reza Pahlavi, has been gaining some popularity. He has been speaking out on X in the last few days, telling his fellow Iranians:

The end of the Islamic Republic is the end of its 46-year war against the Iranian nation. The regime’s apparatus of repression is falling apart. All it takes now is a nationwide uprising to put an end to this nightmare once and for all.

Since the deposition of his father, he has lived in exile in the US. As such, he has been tainted by his close association with Washington and Jerusalem, especially Netanyahu.

If he were to return to power – likely through the assistance of the US – he would face the same problem of political legitimacy as his father did.

What does the future hold?

Iran has never had a long tradition of democracy. It experienced brief instances of liberalism in the first half of the 20th century, but every attempt at making it durable resulted in disarray and a return to authoritarian rule.

Also, the country has rarely been free of outside interventionism, given its vast hydrocarbon riches and strategic location. It’s also been prone to internal fragmentation, given its ethnic and religious mix.

The Shia Persians make up more than half of the population, but the country has a number of Sunni ethnic minorities, such as Kurds, Azaris, Balochis and Arabs. They have all had separatist tendencies.

Iran has historically been held together by centralisation rather than diffusion of power.

Should the Islamic regime disintegrate in one form or another, it would be an mistake to expect a smooth transfer of power or transition to democratisation within a unified national framework.

At the same time, the Iranian people are highly cultured and creative, with a very rich and proud history of achievements and civilisation.

They are perfectly capable of charting their own destiny as long as there aren’t self-seeking foreign hands in the process – something they have rarely experienced.

Amin Saikal, Emeritus Professor of Middle Eastern and Central Asian Studies, Australian National University; and Vice Chancellor’s Strategic Fellow, Victoria University

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