The Challenges Involved in Military Strikes Against Iran’s Nuclear Programme

Two months since Donald Trump’s return to the White House, some of the outlines of the new administration’s approach to the Iran nuclear question are starting to emerge. The door to diplomacy remains open; however, there is also a clear determination to dial up the pressure on Tehran, including through military threats. Among many (though certainly not all) Iran-watchers it has become a truism that decisively destroying the Iranian nuclear programme using military means is not possible and that even limited strikes would be risky and of limited effectiveness. Yet, technical assessments of these claims remain limited. What would a military counterproliferation option look like in practice?

Potential Targets

Counterproliferation strikes against Iran could, in theory, target any number of sites associated with the country’s nuclear programme – including uranium conversion sites, centrifuge production plants and research centres. To have a major material effect, strikes would have to eliminate or seriously degrade Iran’s stocks of fissile material and associated production capabilities. As the programme currently stands, that would mean targeting of Iran’s uranium enrichment capabilities and stocks. Recent intelligence assessments warning of likely Israeli strikes against Iran’s nuclear programme reportedly named Fordow and Natanz – which host enrichment and centrifuge production facilities – as likely targets.

A number of key potential targets – including the Fuel Enrichment Plant (FEP) at Natanz and the Fordow Fuel Enrichment Plant (FFEP) – are located underground. A new facility – currently being constructed inside a mountain south of the main Natanz complex – is expected to house a centrifuge production facility (although some have suggested that it could also be used for uranium enrichment). Causing meaningful damage to these underground facilities would require significant firepower – which presents escalatory risks and practical challenges. The precise depths of Iran’s underground facilities are not publicly known; estimates drawn from public reporting and analysis are included in Table I.

Sites hosting activities that could be relevant to any future weaponisation efforts may also be targeted in counterproliferation strikes. In a major operation against Iran in late October 2024, Israel attacked a facility at Parchin which had previously hosted Iranian weapons-relevant research and which may still have been operational. Much less is publicly known about where any weaponisation-relevant activity may take place; however, Israeli and US intelligence is likely to hold at least some of that information. Past Iranian weaponisation efforts also offer some indication as to facilities that could again play a role in a renewed coordinated pursuit for a nuclear weapons capability. It is reasonable to assume that at least some of that activity would also take place in underground or otherwise hardened sites.

A number of other key facilities are located above-ground and could, in theory, offer somewhat softer targets for potential Israeli or US counterproliferation strikes. These include – among others: the Pilot Fuel Enrichment Plant (PFEP) at Natanz, the as-yet-inoperative Khondab Heavy Water Reactor at Arak, and uranium conversion and fuel fabrication facilities at Esfahan. However, carrying out attacks on these sites would present their own challenges and escalatory risks.

Options and Challenges for Attack

There are a range of weapons available to both the United States military and to the Israeli Air Force that are designed to penetrate significant amounts of reinforced concrete and/or rock and then detonate to destroy or at least badly damage hardened, buried targets. However, the suspected depth of even the FEP would complicate attacks with all but the largest weapons. Furthermore, a number of complicating factors make a weaponeering solution for each facility difficult to arrive at without access to detailed information on the exact hardening measures and layout of each site, and to detailed performance information on each potential strike weapon.

Firstly, the penetration achievable with each weapon will vary greatly depending on the material covering each target. A weapon that can penetrate through tens of meters of packed earth or sand may only penetrate a few meters of standard civilian construction-grade concrete, and even less reinforced, high-density concrete. Furthermore, most of the Iranian facilities are likely to be covered by different layers of reinforced concrete, rock, packed earth and potentially other materials.

The layout of the facility in question is also important for assessing weapon designated point of impact (DPI), explosive payload and fuzing requirements to cause critical damage. For instance, a buried facility that has rooms connected by long narrow shafts with multiple sets of thick blast doors and multiple external entry and exit points would be much harder to guarantee destruction of than a buried facility that has a single large cavern and/or a single entry and exit shaft. A rough outline of the penetrating weapons available to both the United States and to the Israeli Air Force, with their estimated penetration capabilities against a given reinforced concrete layer is included in the table below for context.

To reach even the FEP, assuming that the site is located roughly 8 meters underground and that the covering is predominantly reinforced concrete and/or hard rock, all the weapons available to the Israeli Air Force, and all except the 30,000 lbs GBU-57/B and the 5,000 lbs GBU 72/B available to the United States, would likely require several impacts into the same crater to ‘burrow’ down to the facility and get a weapon through to explode within it successfully. For the FFEP and new facility at Natanz at an estimated 80-100 meters, possibly with layers of reinforced concrete, even the GBU-57/B would likely require multiple impacts at the same aiming point to have a good chance of penetrating the facility. Strikes with lesser penetrating weapons could still collapse entry and exit tunnels given good intelligence about their exact layout and location (with some information already available in open-source satellite imagery analysis). However, unless a longer-term campaign were mounted with regular follow-up strikes, efforts to dig down to the facilities to re-establish access and supplies would likely begin almost immediately.

In addition to physical hardening, any sites that have significant importance to the Iranian nuclear weapons programme would almost certainly have layered ground-based air defences of various kinds stationed around them, especially if an attack was anticipated. Iran possesses a wide range of air defences – most notably Russian S-300PMU-2 long range, as well as indigenous Khordad 15 medium range, and Russian Tor M-1 short range SAM systems. However, the Israeli Air Force emphatically demonstrated its capacity to successfully attack and degrade Iranian air defences, and to successfully carry out a strike against Iran’s nuclear-related sites, in its October 2024 operation. During a more ambitious attack against Iranian nuclear facilities across the country, the IAF would likely be capable of fighting its way into the Iranian air defence system without major issues. With a much larger and more technically advanced set of capability options to bring to bear, the US Air Force (likely alongside the US Navy), would also be able to relatively rapidly degrade and ultimately destroy Iranian air defences to the point where strikes against nuclear facilities could be mounted with minimal risk to aircrew.

Yet, given the presence of short range and medium range SAM systems near most key Iranian targets, some weapons might still be intercepted in flight, particularly free-fall bombs. The Tor M-1 has repeatedly demonstrated the capability to shoot down a range of precision guided munitions in Ukraine, for example. As a highly mobile standalone system with a low signature when not emitting, it is also relatively difficult to reliably track and target from stand-off distances.

The potential presence of pop-up point defence SAMs at each facility means that multiple weapon deliveries might need to be planned against each DPI to ensure the penetrating effects needed. To attack multiple targets across Iran, the IAF alone would almost certainly need to mount a campaign with numerous attack waves to ensure defences could be adequately suppressed and/or destroyed to enable each strike package to achieve the effects required. Even the US Air Force and US Navy might struggle to destroy all the necessary targets in a single attack, while suppressing defences and providing penetrating weapon redundancy in case of attrition from point defences at each target.

Limits of the Military Counterproliferation Option

The practical challenges of carrying out attacks against dispersed and hardened facilities makes clear the infeasibility of relying strictly on a military solution to the threat posed by Iran’s nuclear programme, likely necessitating a major operation to penetrate hardened facilities and/or degrade Iranian air defences. As has been repeatedly argued elsewhere, the highly dispersed nature and advanced state of the Iranian nuclear programme – including extensive latent expertise within the Iranian scientific community – further complicates efforts to eliminate the nuclear programme by military means. For this reason, any comparisons with Israeli attacks against Iraq’s Osirak reactor in 1981 and Syria’s Al-Kibar facility in 2007 are highly misplaced. In both instances, the attacked countries’ programmes were highly concentrated and at a nascent stage, relying extensively on foreign assistance for their development. Following any military strike on its nuclear sites, Iran not only has the requisite indigenous expertise but will also have increased incentive to rebuild, and to rebuild deeper and more hardened facilities.

While destruction of Iran’s nuclear programme by military means is not feasible and even limited strikes carry significant escalatory risks, this does not negate the value of issuing credible military threats as part of a broader effort to roll back the Iranian nuclear programme. Should Iran’s nuclear programme reach a stage where it poses a threat beyond what is acceptable to Israel or the US – for instance, if intelligence was obtained on an Iranian decision to rush towards a nuclear weapon, or even if Tehran decided to begin uranium enrichment to 90% – military attacks could be used to set the programme back to a more acceptable state and may be assessed as being worth the escalatory risks. Making clear the willingness to carry out such attacks – but only as an option of last resort – could help exert the necessary pressure to convince Tehran to cooperate with expectations not to cross certain thresholds or to reverse course on particularly destabilising activity. A thorough consideration of the challenges and risks that following through on any such threats would entail should serve as a sobering reminder that they should not be issued lightly.

© RUSI, 2025.

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