The Islamic Republic of Iran has three core components to its national security policy: its grey zone regional strategy; its unconventional force structure; and its nuclear hedging strategy. In the coming years, each of these will be influenced by: (i) lessons learned from more than four decades of experience, which have largely validated its national security approach; (ii) Iran’s nascent alliance of convenience with Russia; (iii) the policies of the ‘third Iranian republic’ that will emerge after Supreme Leader Ali Khamenei becomes incapacitated or dies, and; (iv) the policies of the US and its partners and how these affect Tehran’s risk calculus.
Iran’s military modus operandi: turning a paler shade of grey
Since its inception, the Islamic Republic has relied extensively on activities in the ‘grey zone’ between war and peace to advance its anti-status quo regional agenda while managing risk, preventing escalation and avoiding war.1 Iran is not unique in this regard. China and Russia have long engaged in grey zone activities, as did the US during the Cold War, although Iran has developed its own unique grey zone modus operandi and toolkit. The latter consists of unilateral and proxy activities, covert or overt, in both the physical and cyber domains. They include: hostage-taking; embassy invasions; terrorism; rocket, drone and missile strikes; and attacks on maritime traffic.
Tehran’s aversion to conventional war and its preference for grey zone activities is not grounded in a transitory calculation of the regime’s interests, or driven primarily by a desire to counter or design-around the US ‘way of war’ (although such considerations undoubtedly play a role).2 Rather, it is a deeply rooted feature of the Islamic Republic’s strategic culture, with its emphasis on ambiguity and indirection. 3 It is also one of the enduring legacies of the long, traumatic and bloody Iran–Iraq War, which reinforced a two centuries-old historical lesson: that conventional wars have often ended badly for Iran.4 The end of the Iran–Iraq War also marked the end of a decade of revolutionary radicalism in Iranian foreign policy. Since then, the Islamic Republic has been much more cautious in its dealings with foreign powers – though risk-averse does not mean risk-avoidant.
Thus, Tehran typically tests adversaries to see what it can get away with. It engages in covert or proxy activities to preserve a degree of deniability and avoid becoming decisively engaged. It relies on incremental action and indirection to create ambiguity regarding its intentions, and to make its enemies uncertain about how to respond. And it arranges its activities in time and space – pacing them (temporally) and spacing them (geographically) – so that adversaries do not feel pressured to respond.5
Yet, Iran will emerge from the grey zone and operate overtly when conditions permit or when deemed necessary. Thus, it conducted small-boat attacks on tanker traffic in the Gulf during the Iran–Iraq War (1980–88) and intervened in Syria’s civil war (2011–present) after concluding that it could do so without prompting US or Israeli intervention. Following the killing of Major General Qassem Soleimani (commander of the Islamic Revolutionary Guard Corps-Qods Force and architect of Iran’s regional strategy) in a US drone strike in January 2020, Tehran responded with a missile strike against US military personnel in Iraq. It openly took credit for the strike as a matter of honour and perceived necessity, given the magnitude of the blow to the regime.
In recent years the Islamic Republic has shown a greater willingness to incur risk and use force unilaterally against Israel, the Gulf Arab states and the US. For instance, it has plotted to kill former senior US government officials (to avenge the killing of Soleimani) and abduct or kill Iranian dissidents in the US, Europe and elsewhere. This increased boldness may be due to: i) the burgeoning influence of the growing number of hardline IRGC officers occupying senior government positions; ii) the failure of the US and its partners to impose significant costs on Iran for its increasingly risk-acceptant behaviour; and iii) Tehran’s loss of control over some of its Iraqi proxies in the aftermath of Soleimani’s death, which may have made it less willing to rely on them for some sensitive operations and activities.6
Force structure: doubling down on (path-dependent) success
Iran’s unbalanced, unconventional force structure – with its emphasis on long-range strike systems (drones and missiles), proxy militias and sea denial capabilities – has served it well. Accordingly, the regime is unlikely to attempt a major military makeover by creating a more conventional, balanced force structure with a large army, air force and navy. Tehran in any case lacks the funds to purchase large numbers of conventional arms, and it is unclear whether potential suppliers would be willing or able to meet such a demand, given Iran’s inability to pay, and the impact this might have on these countries’ ties with the Gulf Arab states.7
So, Tehran will work to increase further the range, accuracy and payload of its drone and missile force. It will also seek to improve its ability to neutralize enemy defences by means other than saturation strikes, developing missile penetration aids and countermeasures (decoys, chaff, low-power electronic countermeasures, or terminal phase manoeuvring, including hypersonic re-entry vehicles).8 The deployment of effective penaids and countermeasures would allow Iran to allocate only one or two missiles per aim point (instead of large salvos). This would yield the functional equivalent of a dramatic increase in its missile inventory, and enable Tehran to enjoy fully the fruits of its accuracy revolution.
Iran will also continue to build up the rocket, drone and missile capabilities of its proxies, and provide its most capable partners (Lebanese Hezbollah, Iraqi groups like Kata’ib Hezbollah, and the Yemeni Houthis) with its most accurate drones and missiles. It will work to enhance their conventional combat capabilities with anti-tank and air defence systems as well. Finally, Iran will continue to slowly expand and modernize its conventional forces, while continuing to harden and bury critical military facilities.9 In particular, Iran may be interested in advanced multi-role fighters like the Su-35, highly capable surface-to-air missiles (SAMs) like the S-400, small naval surface combatants (corvettes and frigates) and midget submarines, imaging satellites and advanced munitions of all kinds.10
Although the emerging axis between Iran and Russia may create new procurement opportunities for Tehran, Moscow will be hard-pressed to spare large numbers of modern arms when its own military is taking heavy losses in Ukraine. Moreover, while Tehran is providing Moscow with hundreds of drones (and maybe missiles as well) costing tens or hundreds of thousands of dollars each, it would like to acquire large numbers of modern weapons systems from Russia costing tens or hundreds of millions of dollars. Thus, the money it earns from drone sales will not buy very many SAMs, fighter aircraft or warships. Furthermore, it is not clear that Iran will be willing to continue transferring large numbers of drones to Russia if tensions with Israel and the US continue to rise. To meet this demand, Iran has reportedly agreed to build a drone production line in Russia.11
Technology transfers are therefore the most likely form of Russian compensation for Iranian assistance. Nevertheless, even limited arms transfers would enable Iran to fill in gaps and selectively modernize its force structure, and to bolster its domestic arms industry by providing modern systems that could be reverse engineered.12
Hedging along the nuclear asymptote – or renewed proliferation?
The Islamic Republic’s nuclear programme dates from the mid-1980s when at the height of the Iran–Iraq War, it started secretly investigating options for producing fissile material and building nuclear weapons. By the late 1990s, fearing that Iraq was reconstituting its nuclear programme, Iran initiated a crash programme to build a bomb.13 After the exposure of its programme in 2002 and the US invasion of Iraq in 2003 (which led Tehran to conclude that it might be next in Washington’s crosshairs), Iran abandoned its crash programme and largely halted weapons work, to avoid giving the US a pretext to invade. It eventually adopted a cautious hedging strategy that has enabled it slowly, incrementally to build an option to manufacture a nuclear weapon, while managing the risks of doing so. This effort has continued to this day as Iran, in asymptotic fashion, gets ever closer to acquiring a nuclear weapons capability.14
Iran adopted a hedging strategy because it had apparently concluded that the potential risks and costs of its crash programme – diplomatic isolation, economic sanctions, a military strike and perhaps a regional nuclear proliferation cascade – might be greater than previously anticipated. 15 This hedging approach is particularly compatible with Iran’s strategic culture, which emphasizes ambiguity, patience and incrementalism to advance the regime’s vital interests, while avoiding escalation and war.
Yet, creating a nuclear option is only one of several vital policy objectives that the Islamic Republic may be pursuing at any given time. Accordingly, Tehran halted (2003) or reversed (2013, 2015) parts of the nuclear programme when it believed these activities jeopardized other important interests (avoiding international isolation and military threats), or when doing so facilitated other goals (preventing diplomatic censure, obtaining sanctions relief, or legitimizing its enrichment programme). Even in these cases, however, the regime continued work on parts of its nuclear programme, as well as its missile programme – the primary delivery means for its planned nuclear force. Senior Iranian policymakers may believe that Iran’s hedging strategy, by creating a latent (nuclear) deterrent, may confer many of the benefits of a nuclear arsenal without the attendant risks and costs.16
Although the Islamic Republic’s long-running nuclear programme has yet to yield a weapon, it may be nearing an inflection point. To pave the way for his succession and implement his programme for the ‘second phase of the Islamic Revolution’,17 Supreme Leader Ayatollah Ali Khamenei has promoted hardliners belonging to or with ties to the IRGC, whose commitment to nuclear hedging is uncertain.18 Thus, a significant number of active and retired senior IRGC officers hold prominent positions in the government of President Ebrahim Raisi and in the current Majles (parliament). These include Vice President for Economic Affairs Mohsen Rezaei, four of 19 cabinet members (including Minister of Interior Ahmad Vahidi and Minister of Intelligence Hojatoleslam Seyed Esmail Khatib), and seven of 12 presidium members of the Majles (including Majles speaker Muhammad Baqer Qalibaf). In addition, seven of 31 provincial governors are serving IRGC officers.
Moreover, the death of Qassem Soleimani may have bolstered the influence of less cautious individuals like the IRGC’s commander-in-chief Hossein Salimi and Aerospace Forces commander Amir Ali Hajizadeh – whose forces were responsible for the September 2019 Aramco attack and the retaliatory strike following Soleimani’s death. 19 People are policy, and Washington should be prepared for the possibility that Tehran may abandon hedging and revert to active proliferation, as part of an effort by Khamenei to confirm his legacy, or by a new leadership intent on forging a new path should Khamenei become incapacitated or die.
Tehran’s nuclear proliferation calculus, then, will depend on whether senior Iranian decision-makers believe that: i) the country’s highly capable conventional drones and missile force and the benefits of latent deterrence obviate the need for nuclear weapons – at least for now; ii) the Islamic Republic can resume weapons research and development activities without getting caught; and iii) the potential risks and costs of getting caught are outweighed by the benefits.20
Nothing succeeds like success; Iran is therefore unlikely to abandon its unconventional force structure. In any case, it lacks the funds needed to purchase large quantities of conventional arms, or suppliers willing to provide them. But this approach has created certain path dependencies, and the Islamic Republic’s heavy reliance on drones and missiles could be a liability if its adversaries were to develop relatively cheap, highly capable defences.21 Likewise, the fragile political and economic circumstances of Lebanon and Iraq impose constraints on Hezbollah and on the Iraqi proxy groups that Iran has cultivated, reducing somewhat their utility as partners or proxies.
The rise of a more risk-acceptant leadership in Tehran in the final stages of Khamenei’s life or after his death may reinforce the regime’s recent tendency towards a greater reliance on overt, unilateral action, while paradoxically creating an environment conducive to independent action by its more venturesome proxies and partners.22 The US and its partners can shape the risk calculus of this emergent leadership in Tehran by responding more assertively to Iran’s destabilizing regional activities. This may also make Tehran more reluctant to transfer drones and missiles to Russia, and to its more independent-minded proxies – at a time of heightened tension with the US and Israel. It could also indirectly encourage Iranian nuclear restraint. After all, if the US and its partners are willing to accept greater risk by pushing back against Iran’s destabilizing regional activities, they are unlikely to remain passive if the Islamic Republic were to attempt a nuclear breakout.
Thus, whether Iran continues with its nuclear hedging strategy or reverts to active proliferation will be influenced, to a significant extent, by the ability of the US and its partners to shape Tehran’s proliferation calculus, and respond effectively to an attempted nuclear breakout. Yet, Iran’s ongoing fissile material build-up and its growing latent (nuclear) deterrent capability remain the most immediate and vexing nuclear challenges – posing dilemmas for which the US and its partners currently lack an adequate response.
This research is supported by the Peace and Conflict Resolution Evidence Platform (PeaceRep), funded by the UK Foreign, Commonwealth and Development Office (FCDO) for the benefit of developing countries. The information and views set out in this publication are those of the authors. Nothing herein constitutes the views of FCDO. Any use of this work should acknowledge the authors and the Peace and Conflict Resolution Evidence Platform.
PeaceRep is a research consortium based at the University of Edinburgh. Our research is rethinking peace and transition processes in the light of changing conflict dynamics, changing demands of inclusion and changes in patterns of global intervention in conflict and peace/mediation/transition management processes.
Consortium members include: Conciliation Resources, Centre for Trust, Peace and Social Relations (CTPSR) at Coventry University, Dialectiq, Edinburgh Law School, International IDEA, LSE Conflict and Civicness Research Group, LSE Middle East Centre, Queens University Belfast, University of St Andrews, University of Stirling, and the World Peace Foundation at Tufts University. PeaceRep is funded by the Foreign, Commonwealth and Development Office (FCDO), UK.
PeaceRep: The Peace and Conflict Resolution Evidence Platform
School of Law, University of Edinburgh, Old College, South Bridge, EH8 9YL
 Eisenstadt, M. (2020), Operating in the Gray Zone: Countering Iran’s Asymmetric Way of War, Policy Focus 162, Washington, DC: Washington Institute.
 For a sophisticated example of this argument, see McInnis, M. (2017), ‘The Strategic Foundations of Iran’s Military Doctrine’, in Gulf Security After 2020, London: International Institute for Strategic Studies, pp. 5–9, https://www.iiss.org/blogs/analysis/2017/12/gulf-security
 The regime has frequently relied on ambiguity, indirection, and proxies to counter domestic political challenges, as well as foreign adversaries. For instance, when the Islamic Republic’s ‘deep state’ sought to undermine reformist president Mohammad Khatami, and later president Mahmoud Ahmadinejad (after he fell out with Supreme Leader Khamenei), it avoided direct attacks on them, assailing instead their supporters and advisors. In the former case, supporters of president Khatami were often attacked in public by the members of the Ansar-e Hezbollah paramilitary group. And while the regime has responded to recent demonstrations with calibrated violence, it has generally contained the unrest by wearing down and demoralizing the protestors. Eisenstadt, M. (2015), The Strategic Culture of the Islamic Republic of Iran: Religion, Expediency, and Soft Power in an Era of Disruptive Change, Middle East Studies Monograph 7, Marine Corps University, November 2015, pp. 4–5, pp. 15–16 , https://www.washingtoninstitute.org/policy-analysis/strategic-culture-islamic-republic-iran-religion-expediency-and-soft-power-era. Social scientists have long noted that individuals from different cultures may display very different preferences regarding the use of ambiguity and indirection, or clarity and directness in interpersonal or intergroup communications and interactions. These cultural differences may well carry over into the realm of conflict and strategy. See, for instance, Bauer, T. (2021), A Culture of Ambiguity: An Alternative History of Islam, New York: Columbia University Press; Alijanian, E. and Dastjerdi, H. V. (2012), ‘The Use of Indirectness Devices in Persian and English Argumentative Written Discourse: A Cross-Cultural Perspective’, International Journal of Linguistics, 4(3), pp. 60–70, https://www.macrothink.org/journal/index.php/ijl/article/view/1733; and Brett, J., Behfar, K. and Sanchez-Burks, J. (2014), ‘Managing Cross-Culture Conflicts: A Close Look at the Implication of Direct Versus Indirect Confrontation’, in Ayoko, O. B., Ashkanasy, N. M. and Jehn, K.A. (eds), (2014), Handbook of Conflict Management Research, Cheltenham, UK: Edward Elgar, pp. 136–54.
 Tabatabai, A. M. (2020), No Conquest, No Defeat: Iran’s National Security Strategy, New York: Oxford University Press, pp. 297–303; Ward, S. R. (2009), Immortal: A Military History of Iran and its Armed Forces, Washington, DC: Georgetown University Press, pp. 325–26.
 Eisenstadt, M. (2021), Deterring Iran in the Gray Zone: Insights from Four Decades of Conflict, Policy Note 103, Washington, DC: Washington Institute, https://www.washingtoninstitute.org/policy-analysis/deterring-America-gray-zone-insights-four-decades-conflict
 For a detailed discussion of the trend towards greater fragmentation among Iran’s proxies in Iraq following the killing of Soleimani and Abu Mahdi al-Muhandis, as well as tensions within the muqawama between the Qods Force’s most trusted Iraqi partners – Kata’ib Hezbollah, Kata’ib Sayyid al-Shuhada, Harakat Hezbollah al-Nujaba – and the more independent armed group Asa’ib Ahl al-Haq, see Knights, M., Smith, C. and Malik, H. (2021), ‘Discordance in the Iran Threat Network in Iraq: Militia Competition and Rivalry’, CTC Sentinel, 14(8), October 2021, https://ctc.usma.edu/discordance-in-the-iran-threat-network-in-iraq-militia-competition-and-rivalry/
 Eisenstadt, M. (2017), ‘Iran after Sanctions: Military Procurement and Force-Structure Decisions’ in Gulf Security After 2020, London: International Institute for Strategic Studies, pp. 11–16, https://www.iiss.org/blogs/analysis/2017/12/gulf-security.
 Rubin, U. and Lorber, A. (1995), ‘Future Trends of Missile Proliferation in the Middle East and Its Impact on Regional Missile Defences’, paper presented at the Eighth American Institute of Aeronautics and Astronautics (AIAA) Multinational Conference on Theater Missile Defense, London, 6–9 June 1995. See also Tasnim News Agency (2022), ‘Iran’s IRGC to Soon Unveil Hypersonic Missile’, 11 November 2022, https://www.tasnimnews.com/en/news/2022/11/11/2802536/iran-s-irgc-to-soon-unveil-hypersonic-missile
 Nadimi, F. (2023), ‘Iran Unveils New Underground Air Base’, Washington Institute PolicyWatch 3700, 13 February 2023, https://www.washingtoninstitute.org/policy-analysis/iran-unveils-new-underground-air-base
 Dugit-Gros, L., Borshchevskaya, A., Eisenstadt, M., Nadimi, F., Rome, H. (2023), ‘After Ukraine: Russia’s Potential Military and Nuclear Compensation to Iran’, Washington Institute PolicyWatch 3693, 20 January 2023, https://www.washingtoninstitute.org/policy-analysis/after-ukraine-russias-potential-military-and-nuclear-compensation-iran
 Nissenbaum, D. and Strobel, W. P. (2023), ‘Moscow, Tehran Advance Plans for Iranian-Designed Drone Facility in Russia’, Wall Street Journal, 5 February 2023, https://www.wsj.com/articles/moscow-tehran-advance-plans-for-iranian-designed-drone-facility-in-russia-11675609087
 Dugit-Gros et al. (2023), ‘After Ukraine: Russia’s Potential Military and Nuclear Compensation to Iran’.
 Albright, D. with Burkhard, S. and the Good ISIS team (2021), ‘Iran’s Perilous Pursuit of Nuclear Weapons’, Washington, DC: Institute for Science and International Security, pp. 23–51.
 Molander, R. C. and Wilson, P. A. (1993), The Nuclear Asymptote: on Containing Nuclear Proliferation, Santa Monica, CA: RAND, https://www.rand.org/pubs/monograph_reports/MR214.html
 Eisenstadt, M. (2022), Iran’s Nuclear Hedging Strategy: Shaping the Islamic Republic’s Proliferation Calculus, Washington Institute Policy Focus 178, 29 November 2022, https://www.washingtoninstitute.org/policy-analysis/irans-nuclear-hedging-strategy-shaping-islamic-republics-proliferation-calculus
 Ayatollah Ali Khamenei (2019), ‘The “Second Phase of the Revolution” Statement Addressed to the Iranian Nation’, Khamenei.ir, 11 February 2019, https://english.khamenei.ir/news/6415/The-Second-Phase-of-the-Revolution-Statement-addressed-to-the.
 Vatanka, A. (2021), ‘Raisi and the Revolutionary Guards’, Iran Primer, U.S. Institute of Peace, 2 September 2021, https://iranprimer.usip.org/blog/2021/sep/02/raisi-and-revolutionary-guards; Golkar, S. and Sawhney, A. (2020), ‘To Secure His Legacy, Khamenei Is Packing Iran’s Government with Young Radicals’, Foreign Policy, 22 July 2020, https://foreignpolicy.com/2020/07/22/iran-khamenei-legacy-youth-washing-radicals-peace-united-states/; Vaisibiame, M. (2020), ‘Iran’s Majlis: A Parliament of IRGC Commanders’, Radio Farda, 2 June 2020, https://en.radiofarda.com/a/iran-majles-a-parliament-of-irgc-commanders/30649083.html
 As of June 2021, almost 600 Iranian fighters (nearly all of them IRGC personnel, including 17 generals) had been killed in action during the Syrian civil war (2011–present), out of an expeditionary force that usually did not exceed more than 1,000 to 1,500 advisers and fighters at any given time; Alfoneh, A., personal correspondence, 10 February and 2 March 2023. These numbers demonstrate the IRGC’s generally tolerant approach to tactical risk, compared to Supreme Leader Ali Khamenei’s usual strategic caution. By contrast, only one US general has been killed in Afghanistan and Iraq since 2001, despite the deployment of hundreds of thousands of US personnel to these combat zones during this period. Rush, R. S. (2014), ‘General and Flag Officers Killed in War’, War on the Rocks, 7 August 2014, https://warontherocks.com/2014/08/general-and-flag-officers-killed-in-war/
 Eisenstadt (2022), Iran’s Nuclear Hedging Strategy.
 Olson, E. A. (2016), ‘Iran’s Path-Dependent Military Doctrine’, Strategic Studies Quarterly (Summer 2016), https://www.jstor.org/stable/26271505#metadata_info_tab_contents. While the US and its partners are fielding increasingly effective drone and missile defences (achieving claimed interception rates of 50 to 90 per cent in Ukraine and Saudi Arabia), they remain very expensive. As a result, the US and its partners still find themselves on the wrong side of the cost-imposition curve.
 Knights, Smith and Malik (2021), ‘Discordance in the Iran Threat Network in Iraq: Militia Competition and Rivalry’.