The United States has launched airstrikes against Iran’s key nuclear enrichment sites, deploying B-2 Spirit stealth bombers to deliver previously unused 30,000-pound bunker-buster bombs.

In a televised address late on 21 June, U.S. President Donald Trump confirmed the attack, stating that the Fordow Fuel Enrichment Plant, Natanz Nuclear Facility, and an unnamed site in Isfahan had been targeted using a combination of air-dropped GBU-57A/B Massive Ordnance Penetrators (MOPs) and Tomahawk cruise missiles launched from U.S. submarines.

President Trump claimed the operation was a “spectacular military success,” saying, “Fordow is gone… All planes are now outside of Iranian airspace. A full payload of bombs was dropped on the primary site.” According to CNN, six B-2 bombers were involved, dropping a total of 12 MOPs on Fordow alone—delivering over 180 tonnes of ordnance.

This marks the first time the GBU-57 has been used in combat. The precision-guided bombs are designed to destroy deeply buried targets, such as fortified nuclear sites, and only the B-2 bomber is capable of carrying them.

The Pentagon has not yet released an official statement detailing the extent of damage, but Iranian state media confirmed that parts of the Fordow facility were hit at approximately 2:30 a.m. local time. The Atomic Energy Organization of Iran described the strike as “a barbaric act that violated international law”, though it added that radiation monitoring showed no signs of contamination at the affected sites.

Iran’s Crisis Management Headquarters reported “no danger to the people of Qom and the surrounding area”, where Fordow is located.

Trump’s unilateral action drew mixed reactions in Washington. Most Congressional Republicans expressed support for the strikes, while many Democrats and some Republicans questioned their legality, arguing that the President had not obtained congressional authorisation for military action.

The broader international response has been one of concern, with analysts warning of unpredictable Iranian retaliation. The region had already been on high alert following Israeli airstrikes on 12 June. U.S. bases in the Middle East had been bracing for reprisals, and B-2 bombers were recently deployed to Guam in anticipation of potential operations.

Despite earlier signals that diplomatic options remained on the table, Trump’s decision appears to have been influenced by urgent appeals from Israeli leaders, who reportedly told the White House they could not wait for extended negotiations.

ABC News reported that the attack closely mirrored a joint U.S.-Israeli exercise conducted in 2024, which simulated a strike on hardened nuclear sites. Axios noted that top Republicans in Congress were briefed in advance of the operation, but top Democrats were not.

Iran’s nuclear programme has long been a point of contention between Tehran and Western powers. While the U.S. intelligence community has previously stated it does not assess Iran to be actively pursuing nuclear weapons, Trump has maintained that Iran must be prevented from acquiring such capability at all costs.

President Trump warned in a Truth Social post following the strikes: “Any retaliation by Iran against the United States of America will be met with force far greater than what was witnessed tonight.”

Security was heightened in major U.S. cities in response to fears of retaliatory attacks. Meanwhile, Israel temporarily closed its airspace, signalling concern about escalation.

The American B-2 stealth bomber is the only plane capable of carrying the bombs needed to strike Iran’s deepest nuclear facilities, but the decision to use them is not without risk.

It sounds so surgical, so precise, exactly the kind of air attack that only the U.S. Air Force can execute.

A series of B-2 bombers lifts off from Whiteman Air Force Base in Missouri or the island of Diego Garcia in the Indian Ocean. Refueled in the air, they head for a remote mountain in north-central Iran, far from civilians, where they get Iran’s most heavily fortified nuclear site, Fordo, in their sights.

They drop their giant 30,000-pound bunker-busters, one after another, blasting a giant hole down to the centrifuge halls that have been in the bull’s-eye of the American military since President Barack Obama and the leaders of Britain and France revealed the existence of the plant in the fall of 2009, charging Iran with a great “deception.”

Few potential operations, with the possible exception of a Chinese invasion of Taiwan, have been so examined, rehearsed and debated. Technically, the military and geological experts say, it should be doable.

And yet it is full of risks — known unknowns and unknown unknowns, as the former defense secretary Donald Rumsfeld used to say in the context of the Iraq War, another rabbit hole of American military action in the Middle East. That is why it has given pause to every American president who has looked at it for the past 16 years.

President Trump on Wednesday emphasized that he had yet to make a decision to drop what in private he calls “the big one.” But gone was the bellicose tone that characterized his public utterances a day earlier. In its place was a note of caution. “I may do it,” he told reporters on the White House’s South Lawn. “I may not do it. I mean, nobody knows what I’m going to do.”

Meanwhile, the Iranians, after five days of remarkable losses to the Israelis, seemed to be looking for a way out. Iran’s supreme leader, Ayatollah Ali Khamenei, issued a defiant response to Mr. Trump’s call for “unconditional surrender,” but Mr. Trump said there were indications that the Iranians wanted to talk, and reports of an official Iranian plane landing in Oman, where many of the negotiations with Steve Witkoff, the president’s special envoy, had taken place before Israel’s attack.

If Mr. Trump is taking a pause, it may be because the list of things that could go wrong is long, and probably incomplete. There’s the obvious: It’s possible that a B-2 could get shot down, despite Israel’s success of taking out so many of Iran’s air defenses. It’s possible the calculations are wrong, and even America’s biggest conventional bomb can’t get down that deep.

“I’ve been there, it’s half a mile underground,” Rafael Grossi, the director general of the International Atomic Energy Agency, said last week, as the Israeli operation began.

But assuming that the operation itself is successful, the largest perils may lie in the aftermath, many experts say, just as they did in Afghanistan and Iraq. There are many lessons from that ugly era of misbegotten American foreign policy, but the most vital may be that it’s the unknown unknowns that can come back to bite.

Iran has vowed that if attacked by American forces, it would strike back, presumably against the American bases spread around the Middle East and the growing number of assets gathering in the Persian Gulf and the Mediterranean. All are within missile range, assuming Iran has missiles and launchers left after the Israelis are done with their systematic targeting.

Of course, that could start a cycle of escalation: If Americans are killed, or even injured, Mr. Trump will be under pressure to exact revenge.

“Subcontracting the Fordo job would put the United States in Iran’s sights,” Daniel C. Kurtzer, a former U.S. ambassador to Israel, and Steven N. Simon, a veteran of the National Security Council, wrote in Foreign Affairs on Wednesday. “Iran would almost certainly retaliate by killing American civilians. That, in turn, would compel the United States to reciprocate.”

“Soon enough,” they continued, “the only targets left for Washington to hit would be the Iranian regime’s leaders, and the United States would again go into the regime-change business — a business in which exceedingly few Americans want to be involved any longer.”

The reaction could take other forms. Iran is skilled at terrorism, and reacted to the U.S.-Israeli cyber attack on its nuclear program 15 years ago by building a fearsome cyber corps, not as stealthy as China’s or as bold as Russia’s, but capable of considerable damage. And it has plenty of short-range missiles left to attack oil tankers, making transit in the Persian Gulf too risky.

The last thing the White House wants to do is air these risks in public. Democrats are calling for a congressional role, but they have no power to compel it. “Given the potential for escalation, we must be brought into this decision,” Senator Adam B. Schiff of California, one of Mr. Trump’s political rivals, said on CNN on Wednesday. “Bombing Fordo would be an offensive activity.”

And like most offensive activities, there are longer-term perils, beyond the cycle of attack and retaliation.

Already, the message of these past five days, as interpreted by Iranian leaders or others with nuclear skill, may well be that they should have raced for a bomb earlier, and more stealthily. That was what North Korea did, and it has now ended up with 60 or more nuclear weapons, despite years of American diplomacy and sabotage to stop it. It is a big enough arsenal to assure that its adversaries, South Korea and the United States, would think twice about conducting the kind of operation that Israel executed against Iran.

And history suggests that nuclear programs can be bombed, but not eliminated.

“Nuclear weapons can be stopped through force — the Syrian program is a good example,’’ said Gary Samore, who was the Obama administration’s coordinator for weapons of mass destruction when the existence of the Fordo plant was made public. (It was discovered toward the end of the Bush administration.)

And in Iraq, after the Israelis bombed the Osirak reactor in 1981, to keep Saddam Hussein from getting the fuel for a bomb, the Iraqis “reacted by building a huge, secret program” that went undetected until after the Gulf War in 1991, Mr. Samore said. That was such an embarrassment to American intelligence agencies that more than a decade later they wildly overestimated his ability to do it again, contributing to the second failure — and leading the United States into the Iraq war.

But Mr. Samore added: “I can’t think of a case where air power alone was sufficient to end a program.”

That is an important consideration for Mr. Trump. He must decide in the next few days whether Israel’s attacks on Iran’s Natanz enrichment facility, and its bombing of workshops where new centrifuges are made and laboratories where weapons research may have been taking place, are sufficient to set back the Iranian program.

In short, he must decide whether it is worth the huge risk of direct American involvement for whatever gain would come from destroying Fordo with American pilots, American warplanes and American weapons.

But he also doesn’t want to be accused of missing the chance to set the Iranians back by years. “If this war ends and this Fordo is left intact,” said Mr. Samore, now a professor at Brandeis University, “then it wouldn’t take long to get this going again.”

Mr. Trump has not weighed these questions in public, and it is always hard to know how he is assessing the evidence. He bristled the other day, on Air Force One, when a reporter noted to him that his own director of national intelligence, Tulsi Gabbard, had testified in Congress just a few months ago that Iran had made no decision to produce a bomb, even if its fuel production had surged.

He insisted that there wasn’t much time left — though he cited no evidence to contradict his own intelligence chief.

“Don’t forget, we haven’t been fighting,” Mr. Trump said Wednesday in the Oval Office. “We add a certain amount of genius to everything, but we haven’t been fighting at all. Israel’s done a very good job today.”

Then, muddying the waters anew, he turned to his signature phrase: “But we’ll see what happens.”

Prime Minister Benjamin Netanyahu of Israel at United Nations General Assembly last year. Experts believe that Israel has been expanding its secretive nuclear program.

The war that Israel launched against Iran seeks to take out its nuclear program, which much of the world views with alarm and experts say is growing to the point that it could make an atomic weapon within months.

Israel has its own secretive nuclear weapons program, one that it doesn’t publicly acknowledge but that, some experts believe, is also expanding.

“From an official diplomatic posture perspective, the Israelis will not confirm or deny” their nuclear arsenal, said Alexander K. Bollfrass, a nuclear security expert at the International Institute for Strategic Studies in London.

Instead, Israel has said it will not be the first country to “introduce” nuclear weapons to the Middle East. That deliberately vague wording amounts to what Mr. Bollfrass called an “obfuscation over what is clearly an established nuclear weapons program.”

How big is Israel’s nuclear arsenal?

Israel is widely believed to have at least 90 warheads and enough fissile material to produce up to hundreds more, according to the Center for Arms Control and Nonproliferation and the Nuclear Threat Initiative.

The International Atomic Energy Agency, the nuclear watchdog for the United Nations, has assessed that 30 countries are capable of developing nuclear weapons but only nine are known to possess them. Israel has the second-smallest arsenal among the nine, ahead only of North Korea, according to a Nobel Prize-winning advocacy group, the International Campaign to Abolish Nuclear Weapons. Israel could fire warheads from fighter jets, submarines or ballistic missile ground launchers, experts said.

Israel is one of five countries — joining India, Pakistan, North Korea and South Sudan — that is not a signatory to the U.N. Nuclear Nonproliferation Treaty. The agreement, which came into force in 1970, generally commits governments to promoting peaceful uses of nuclear energy and preventing the spread of nuclear weapons.

(Iran is a signatory to the treaty, although Israel and world powers have accused Tehran of violating it by unnecessarily enriching uranium at high enough levels to build a nuclear weapon.)

Israel would have to give up its nuclear weapons to sign the treaty, which recognizes only five countries as official nuclear states: Britain, China, France, Russia and the United States — the permanent members of the U.N. Security Council. All had detonated a nuclear weapon by 1967, the cutoff date in the treaty to qualify for the designation.

How long has Israel had nuclear weapons?

Israeli leaders were intent on building a nuclear arsenal to safeguard the country’s survival soon after it was founded in 1948 in the wake of the Holocaust, historical records indicate.

The Israel Atomic Energy Commission was established in 1952, and its first chairman, Ernst David Bergmann, said that a nuclear bomb would ensure “that we shall never again be led as lambs to the slaughter,” according to the Jewish Virtual Library.

Israel began building a nuclear weapons development site in 1958, near the southern Israeli town of Dimona, researchers believe. A recently declassified U.S. intelligence report from December 1960, by the Joint Atomic Energy Intelligence Committee, stated that the Dimona project included a reprocessing plant for plutonium production. The report concluded that the project was related to nuclear weapons.

Image Part of the nuclear power plant near Dimona, Israel, in 2014. The site has long been a symbol of fascination and, to some, anger over Israel’s nuclear weapons program. Credit… Jack Guez/Agence France-Presse — Getty Images

Around 1967, Israel secretly developed the ability to build nuclear explosives, according to the Arms Control Association. By 1973, the United States “was convinced Israel had nuclear weapons,” the Federation of American Scientists later wrote.

Israel is not among the three dozen countries — all in Europe or Asia — considered to be protected by the United States’ so-called nuclear umbrella. That protection not only serves as an American deterrent against adversaries but also aims to encourage the countries not to develop their own nuclear weapons.

Experts said that the fact that Israel was not part of the American nuclear umbrella was another unspoken acknowledgment that Israel had its own atomic weapons and did not need protection or deterrence.

“Ultimately, there is a sense of responsibility that Israel’s security rests with Israel, and they will do what is necessary to provide for that,” Mr. Bollfrass said.

Has Israel used its nuclear weapons in war?

No.

The Jewish Virtual Library, which is considered among the world’s most comprehensive Jewish encyclopedias, has cited reports that Israel prepared its nuclear bombs during the Arab-Israeli wars of 1967 and 1973, but the weapons were not used.

There have been a few reports over the past 50 years that Israel has tested its nuclear weapons at underground sites, including in the Negev desert in southern Israel.

The most prominent episode — and one that remains under debate — was in September 1979, when an American satellite designed to detect nuclear explosions reported a double flash near where the South Atlantic and Indian oceans meet. Some scientists believed that the double flash was likely to have been the result of a nuclear test, by Israel or South Africa, or possibly by both.

Image The International Atomic Energy Agency headquarters in Vienna, Austria. There is no agreement with Israel that would allow the U.N. watchdog agency to monitor the nuclear site in Dimona, according to experts. Credit… Joe Klamar/Agence France-Presse — Getty Images

Israel denied involvement in what is known as the Vela incident, for the satellite’s name. Former President Jimmy Carter’s White House diaries, published in 2010, cited “growing belief” at the time that Israel had tested a nuclear explosion near the southern tip of South Africa. But that was never proven, and “relevant documents for the Vela incident are still classified,” the scientists Avner Cohen and William Burr wrote in 2020, citing the diaries.

Where does Israel build its nuclear weapons?

It’s widely believed that Israel’s nuclear weapons program is housed in Dimona.

Experts said it appeared that inspectors from the International Atomic Energy Agency had never been to the site, and that there was no agreement with Israel that would allow the U.N. watchdog agency to monitor it. American scientists visited Dimona in the 1960s and concluded that the nuclear program there was peaceful, based on increasingly limited inspections, historical records show. But there is no public evidence that American inspectors have been back since.

Satellite photos show new construction at Dimona over the past five years. At a minimum, experts said, the facility is undergoing repairs and much-needed modernization.

There is also a growing belief among some experts that Israel is building a new reactor in Dimona to increase its nuclear capability. A report released this week by the Stockholm International Peace Research Institute said Israel appeared to be upgrading a reactor site there to produce plutonium, which can be used both for nuclear weapons and some peaceful purposes, like in space.

Because of its secrecy, Dimona has long been a symbol of fascination and, to some, anger over Israel’s nuclear weapons program.

In a rare public event at the site in 2018, Prime Minister Benjamin Netanyahu of Israel used it as a backdrop to warn enemies that “those who threaten to wipe us out put themselves in a similar danger — and in any event will not achieve their goal.”