Will Iran Get the Bomb?

More than a month after the Israeli and US attacks on Iran’s nuclear facilities and scientists, the full extent of the damage to the Iranian nuclear programme remains unclear. Intelligence assessments vary. Despite the Trump White House’s assertions that the military strikes ‘obliterated’ Iran’s nuclear programme, US and even Israeli intelligence assessments are more conservative. The Pentagon and Israeli officials have estimated that the programme has been set back by up to two years; another US intelligence assessment suggests that Iran could start enriching uranium again in a matter of months. Broadly speaking, the consensus appears to be that the programme has not, in fact, been definitively destroyed.

Yet, the exact extent of the material damage to the programme is secondary. As others have detailed, Iran does not have to reconstitute the whole of its programme to be able to produce a nuclear weapon and could, in fact, probably do so relatively quickly, should it decide to. The more important – and, arguably, more challenging – question is over the impact of the ‘twelve-day war’ on Iran’s assessments and decision-making as to the value and feasibility of developing a credible nuclear deterrent.

The Drive for the Ultimate Deterrent

Recent developments have probably reinforced incentives for Iran to pursue a nuclear weapon, which predate the recent escalation in violence. Namely, the attacks have made painfully clear the ineffectiveness of Iran’s other capabilities to deter and defend against attacks on its territory. Iran has historically relied on a strategy of ‘forward defence’, using proxies and allies across the Middle East to help ensure that threats to its security were kept away from Iran’s borders. Its missile capabilities were meant to serve as an additional deterrent against attack and as a recourse for dealing with threats away from Iranian territory.

In light of the Israeli degradation of both Hamas and Hizbullah and following the underwhelming performance of Iranian missiles in direct exchanges with Israel in 2024, the limitations of both aspects of Iran’s ‘forward defence’ strategy have become clear. At the same time, the failure of Iranian air and missile defence in defending against Israeli and US attacks – during the ‘twelve-day war’ and in earlier exchanges – have further highlighted Iran’s vulnerability.

Furthermore, whereas Tehran may have previously assumed that a near-threshold nuclear programme would be sufficient to deter attacks against its territory, the events that have unfolded since 13 July will have disabused Tehran of that belief. The scale of the Israeli attacks, the range of targets that were hit, and the willingness of the US to actively support Israeli military action against Iran will have reinforced the credibility and seriousness of the military threat Iran faces from its adversaries, already a problem in a regime that mixes paranoia into its desire to survive. Veiled threats – both by Israeli and US leadership – against Iran’s Supreme Leader and the regime as a whole will further aggravate threat perceptions in Iran, even if the US is now back to focussing on talks.

In light of these increasingly credible threats to Iranian security [MS1] and the regime, as well as the apparent ineffectiveness of Iran’s current deterrence strategy and capabilities, it is reasonable to assume that Iran is more incentivised than ever to pursue the ultimate deterrent and push towards a nuclear weapons capability. Much will depend on Iran’s calculations around what is now necessary to deter Israeli strikes. Iran’s thinking on this after 7 October 2023 failed to take account of Israel’s shock, seemingly assuming that the existing ‘rules of the game’ could be sustained, and that Israel would continue to tolerate the existence of Hizballah and its missile force on its northern border. In reality, Israel not only regarded this as unacceptable, but had developed the intelligence access to make first-mover advantage really count, a feat repeated in the direct campaign against Iranian leadership, air defence and missile capabilities and stockpiles.

Easier Said Than Done

However, intent to develop a nuclear deterrent is not sufficient; a would-be proliferator must also have the capability to do so. Here, of relevance is not simply the technical know-how, equipment and materials but also the organisational, doctrinal and other supporting components. A nuclear weapon is, after all, not the same as a credible nuclear deterrent. While Iran may have been – and probably still is – within relatively quick reach of the first, it is a long way from the second. Pursuing the former without securing all the components necessary for the latter would leave Iran in an exceptionally vulnerable position.

First, a single nuclear warhead – or even a small arsenal of nine or ten nuclear weapons (a somewhat arbitrary hypothetical, based on the amount of highly enriched uranium that remains unaccounted for following the attacks on Iran’s nuclear sites) – would not be a survivable deterrent. Such a small stockpile would be immediately targeted by Israel and, probably, the United States.

It is difficult to assess the size of the nuclear weapons arsenal that Iran would have to develop before it could be assumed to have a survivable second-strike capability. Israel is estimated to possess about 90 nuclear warheads with sufficient fissile material to produce an estimated 200 weapons, as well as superior air and missile capabilities. That is saying nothing of US nuclear and conventional counterforce capabilities. Acquiring a nuclear capability that could survive a pre-emptive Israeli or US strike – or at least create sufficient doubt in Israel and the US over their ability to eliminate an Iranian arsenal in such a strike – will not necessarily require Iran to obtain warhead parity. However, it would necessitate possession of a sizeable and distributed arsenal. Any concerted campaign to produce deliverable nuclear weapons at scale would almost certainly be picked up by Israeli or US intelligence and targeted.

Besides the challenge of successfully attaining a survivable second-strike capability, a credible Iranian nuclear deterrent would also be predicated on bolstered conventional capabilities. First and foremost, this would require the reconstitution and improvement of Iranian air and missile defences to defend against Israeli pre-emptive or retaliatory strikes in case of an escalation to a nuclear exchange. As the ‘twelve-day war’ and, indeed, the last year have demonstrated, Iran’s air and missile defences are unable to meet the requirements of defending Iran against a concerted Israeli attack. Existing air and missile defence capabilities have been further degraded as a result of these strikes. According to Israeli estimates, the ‘twelve-day war’ decimated about a third of Iran’s pre-war missile defence systems, although Tehran claims to have replaced damaged systems.

Furthermore, Iran currently lacks sufficient advanced conventional capabilities to give it meaningful conventional deterrence and escalation options short of resorting to nuclear weapons use in the instance that it decided to acquire a nuclear weapons capability. In the case of North Korea, before Pyongyang had sufficient conventional missile capabilities and numbers to deter a pre-emptive South Korean strike against its nascent nuclear capability, it maintained a massive conventional force giving it options for escalation. In that case, a large buildup of conventional artillery able to directly target Seoul.

While Iran has the most diversified and advanced missile arsenal in its region, for now its deterrent effect has been severely undermined by its relatively limited performance over the past 18 months. This is not to say it has no value: media reporting paints a picture of Israeli and US interceptor capacity being severely tested, and analysis suggests as Iran diversified its targets that smaller salvoes later on in the war had slightly higher success rates. But its current ability to pose a direct threat to Israel has been hugely curtailed, leaving other escalatory options like threatening the Strait of Hormuz (at a cost to its own exports) or attacking US and other international forces in the region. Both are high-risk options at a time of extreme vulnerability.

Finally, a nuclear capability will remain ineffective so long as Iran has not devised the organisational mechanisms and doctrinal precepts to deploy it. Which part of Iran’s defence and security structure will be responsible for fielding nuclear-armed missiles? What would the decision-making process look like for authorising nuclear use? Currently, the Islamic Revolutionary Guard Corps (IRGC) Aerospace Force is believed to have primary responsibility over Iran’s missile forces, including the missiles in Iran’s arsenal which are believed to be nuclear-capable. This could remain the case should Iran decide to arm its missiles with nuclear payloads. Launch authority would probably rest with the Supreme Leader. However, Iran may also choose to segregate responsibility over its nuclear and conventional forces to ensure resilience in – and complicate adversarial assessments over – its nuclear firing chain. There is also the question of what role Iran would assign to its nuclear forces in its overall deterrent strategy. All these questions and more will need to be addressed before Iran is able to effectively field a nuclear deterrent.

Between a Rock and a Hard Place

As such, Tehran is faced with a serious dilemma in its decision-making on whether to pursue a nuclear weapons capability as a last-ditch effort to restore deterrence or to cut its losses and – at most – continue hoping that its current nuclear programme or some reconstituted version of it will be enough to prevent further aggression against it. While the incentives for Iran to develop a nuclear weapon are clear, so are the challenges. However, it is unclear to what extent Tehran appreciates these challenges and what the Iranian leadership may be desperate or delusional enough to attempt if it feels it has no other choice. Alongside the offer of diplomatic offramps, the US and E3 (the UK, Germany and France) should also be making clear to Tehran just how difficult it will be for Iran to attain a credible and effective nuclear deterrent, not just a nuclear weapon.

More broadly, Tehran will need to consider whether any nuclear deterrent it is able to produce will be any more effective than Israel’s has been thus far. The latter neither prevented Hamas from attacking, nor dissuaded the Iranians in their missile assault. Although the manner and end to which Iran may employ a nuclear deterrent would probably differ from that of the Israelis, questions over the effectiveness of nuclear deterrence in regional security dynamics remain salient.

© RUSI, 2025.

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