How difficult is building a nuclear weapon? Experts weigh in after Iran strikes

Last month, President Donald Trump ordered U.S. airstrikes on several of Iran’s nuclear facilities, declaring afterward that the attacks had “obliterated” the country’s nuclear program. Yet, according to early U.S. intelligence assessments, the strikes appear to have only delayed Iran’s progress by a few months.

This episode spotlights a fundamental question: How difficult is it in 2025 — 80 years after the Manhattan Project — for a nation to build a nuclear weapon?

To find out, McClatchy News spoke with six nuclear proliferation experts. They described the process of constructing an atomic weapon as a complex operation that requires three major stages — some of which are substantially more challenging than others.

“On average, states that have acquired nuclear weapons have taken about 10 years to do it, so it’s certainly not easy,” Nicholas Miller, a professor of government at Dartmouth University, told McClatchy News.

Step 1: Fissile material

“The first step — obtaining the fissile material — is widely seen as the most difficult,” Matthew Fuhrmann, a professor of political science at Texas A&M University, told McClatchy News.

Fissile material is the explosive fuel used in a nuclear weapon. Depending on the type of weapon, this material can be composed of highly enriched uranium, bomb-grade plutonium or heavy hydrogen.

In order to make this material ready for use inside a nuclear weapon, highly sophisticated processes are required.

For example, weapons-grade uranium is produced by mining, processing, and then enriching uranium to a high degree, according to the Union for Concerned Scientists. Weapons-grade plutonium, on the other hand, is created by irradiating uranium in a nuclear reactor and then chemically separating the plutonium produced from the spent fuel.

Aside from the technical know-how, there are other obstacles to creating fissile material, experts said.

“Since the 1970s, the international community has made it more and more difficult to acquire the enrichment or reprocessing technology needed to make this material,” Miller said.

Because of this, countries seeking out nuclear weapons often must turn to black markets or other clandestine methods in order to obtain the raw materials for fissile material — which is time-consuming and expensive.

“Even if they manage to get their hands on the necessary technology, countries face intense pressure not to use it for nuclear weapons, as we have witnessed with Iran over the last few decades,” Miller said.

Further, nations set on developing nuclear weapons can be subject to covert operations or outright military attacks, which can slow them down considerably.

“Before the U.S. and Israeli attacks against Iran’s nuclear facilities, Tehran faced cyberattacks against its uranium enrichment program, for example,” Fuhrmann said.

Step 2: Weaponization

The second stage, weaponizing the fissile material, is generally more straightforward than the first, experts said.

“No one pretends that nuclear weapons design secrecy is an obstacle at all,” Sharon Squassoni, a professor of international affairs at George Washington University, told McClatchy News.

“The knowledge of how to design a simple nuclear bomb, the ‘gun-type’ bomb used at Hiroshima, has been widely known for years,” according to Scott Sagan, the co-director of Stanford University’s Center for International Security and Cooperation.

The gun-type bomb — the most basic nuclear weapon — entails using conventional explosives to fire a subcritical piece of fissionable material into another piece to then trigger the explosive nuclear reaction.

This technology “was considered so reliable that it was not fully tested in advance” of the U.S. dropping the first-ever nuclear bomb on Hiroshima in 1945, Miller said.

Given the relative ease of this step, it has been estimated to take about six months to develop, Squassoni said.

However, creating more advanced weaponization techniques — for example, miniaturized warheads — is substantially harder, requiring several years, Miller said.

Safety concerns can complicate the timeline in this step. Doing things safely to ensure the weapons won’t accidentally detonate early takes time.

“If a country was planning to build and immediately use a weapon, they would probably be willing to take safety-related shortcuts, decreasing its timeline to some degree,” Furhmann said.

Step 3: Delivery system

The final step is creating or obtaining a device to deliver the weapon to its target. This can be easy or extremely difficult, depending on the type of device being sought out, experts said.

The weapon could simply be placed on a barge or a train, methods which do not require much know-how, but it would forgo the element of surprise, Elena Sokova, the executive director of the Vienna Center for Disarmament and Non-Proliferation, told McClatchy News.

A country could also use a plane to drop a warhead — like the U.S. did in its bombing of Hiroshima.

“This could be done quickly once a state had enough fissile material, probably within 6-12 months,” Fuhrmann said. But, a plane would be vulnerable to an enemy’s air defenses.

The most dependable delivery systems, though, are ballistic missiles in addition to submarines and strategic bombers, Sokova said, noting it takes years to develop these more sophisticated capabilities.

To this point, only small warheads would fit on a ballistic missile, so the simpler gun-type device would not work.

Prevention

The U.S. strikes on Iran also raise another important question: Can the use of force effectively prevent the development of nuclear weapons? Or is there a better alternative?

Several experts agreed that military action cannot stop a country that is determined to go nuclear over the long term.

“You can’t prevent the resurgence of a nuclear program by bombing nuclear facilities,” Sokova said. “The bombing will throw back the program and delay it, but if a country is determined to develop nuclear weapons, the potential for the re-constitution of the program will remain.”

Nancy Gallagher, the director of University of Maryland’s Center for International and Security Studies, echoed this sentiment.

“Supply-side counter proliferation strategies (i.e., trying to deny countries the knowledge, material, and equipment needed to make deliverable nuclear weapons) cannot permanently prevent proliferation and may increase motivation to acquire nuclear weapons,” Gallagher told McClatchy News.

Instead, the best way to stop the spread of nuclear weapons, according to Gallagher and Sokova, is through diplomacy, specifically the 1968 Nuclear Nonproliferation Treaty.

The landmark treaty set up safeguards through the International Atomic Energy Agency (IAEA) to monitor compliance and stop nuclear materials from being diverted for weapons, while guaranteeing all signatories equal access to nonthreatening nuclear technology.

This story was originally published July 8, 2025 at 12:29 PM with the headline "How difficult is building a nuclear weapon? Experts weigh in after Iran strikes."