News | March 19, 2021

Iran’s Gray Zone Strategy: Cornerstone of its Asymmetric Way of War

By Michael Eisenstadt PRISM Vol. 9, No. 2

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Michael Eisenstadt is Kahn Fellow and Director of the Military and Security Studies Program at The Washington Institute for Near East Policy.

(Mohammad Ali Dahaghin, February 19, 2020)
(Mohammad Ali Dahaghin, February 19, 2020)
(Mohammad Ali Dahaghin, February 19, 2020)
(Mohammad Ali Dahaghin, February 19, 2020)
(Mohammad Ali Dahaghin, February 19, 2020)
Photo By: Mohammad Ali Dahaghin
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Since the creation of the Islamic Republic in 1979, Iran has distinguished itself (along with Russia and China) as one of the world’s foremost “gray zone” actors.1 For nearly four decades, however, the United States has struggled to respond effectively to this asymmetric “way of war.” Washington has often treated Tehran with caution and granted it significant leeway in the conduct of its gray zone activities due to fears that U.S. pushback would lead to “all-out” war—fears that the Islamic Republic actively encourages. Yet, the very purpose of this modus operandi is to enable Iran to pursue its interests and advance its anti-status quo agenda while avoiding escalation that could lead to a wider conflict. Because of the potentially high costs of war—especially in a proliferated world—gray zone conflicts are likely to become increasingly common in the years to come. For this reason, it is more important than ever for the United States to understand the logic underpinning these types of activities, in all their manifestations.

Gray Zone, Asymmetric, and Hybrid “Ways of War” in Iran’s Strategy

Gray zone warfare, asymmetric warfare, and hybrid warfare are terms that are often used interchangeably, but they refer neither to discrete forms of warfare, nor should they be used interchangeably—as they often (incorrectly) are. Rather, these terms refer to that aspect of strategy that concerns how states employ ways and means to achieve national security policy ends.2 Means refer to the diplomatic, informational, military, economic, and cyber instruments of national power; ways describe how these means are employed to achieve the ends of strategy. The terms gray zone, asymmetric, and hybrid thus refer to the “ways of war”—how these instruments are used—though the term hybrid has a dual character and also refers to means. (For a graphic depiction of how these concepts apply to Iran’s strategy, see figure 1 below.)

Figure 1: Iran’s Gray Zone Strategy
Figure 1: Iran’s Gray Zone Strategy
Figure 1: Iran’s Gray Zone Strategy
Figure 1: Iran’s Gray Zone Strategy
Figure 1: Iran’s Gray Zone Strategy
Photo By: NDU
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Nearly all state actors (including the United States) engage in gray zone activities, leverage asymmetries, and are hybrid actors, at least to some extent. Many states operate in the gray zone, at least occasionally, to manage risk, limit escalation, and avoid war. All states employ asymmetries to gain advantage and achieve disproportionate effects. And nearly all states create hybrid organizational designs and act, to some extent, in a hybrid fashion to accrue advantage and achieve synergies. Yet, for some states, the gray zone modus operandi defines nearly everything they do. Gray zone strategies are inherently asymmetric (see below) and often make extensive use of hybrid modes of operation. Iran is the quintessential gray zone actor whose entire modus operandi is influenced by this particular way of war, and whose default approach is to operate in the gray zone—except when fighting “imposed wars” like the Iran-Iraq War and the Syrian civil war. However, even in such cases, its approach to conventional operations is often tinged by its gray zone modus operandi, with its emphasis on proxy action and hybrid activities.

The Gray Zone

Gray zone actors probe and test to determine what they can get away with. They rely on covert or unacknowledged proxy activities to preserve deniability and avoid becoming decisively engaged with the adversary. They rely on incremental action to create ambiguity regarding their intentions, and to make their enemies uncertain about how to respond. And they arrange their activities in time and space—pacing and spacing them so that adversary decisionmakers do not overreact. This enables them to challenge stronger adversaries and advance their anti-status quo agendas while managing risk, avoiding escalation, and preventing war.3

The Islamic Republic has always understood that its long-term goal of becoming the dominant power in the Middle East would bring it into conflict with the United States (whose influence in the region it seeks to eradicate) and Israel (which it seeks to eliminate). Accordingly, it developed a modus operandi that has enabled it to advance its anti-status quo agenda while avoiding war with either. Tehran’s interest in avoiding war is not grounded in a transitory calculation of the regime’s interests: it is a deeply rooted feature of the regime’s strategic culture that is reflected in Iranian strategy under Supreme Leader Ayatollah Ali Khamenei. This is one of the enduring legacies of the 8-year-long Iran-Iraq War. Nearly a quarter-million Iranians were killed in that conflict, and the wounds have still not healed.4 Iran is determined to never again repeat that experience.5

Iran’s gray zone strategy works by leveraging a number of asymmetries pertaining to differences in the way that Tehran and Washington think, organize, and operate on the policy and strategic levels. The most important of these asymmetries is conceptual. U.S. decisionmakers tend to conceive of war and peace with Iran, as well as with other state actors like China and Russia, in stark, binary terms, and have frequently been constrained by fear of escalation. This creates opportunities for Iran (and others) to act in the gray zone “in between.” (The main exception here—by and large, a relatively recent one—is in the cyber domain.6) By contrast, Tehran tends to see conflict as a continuum. The key terrain in gray zone conflicts then is the gray matter in the heads of American policymakers who believe that a local clash could somehow rapidly escalate to an “all-out” war. The result is often U.S. inaction, which provides gray zone operators like Iran with greater freedom to act.


In addition to the aforementioned conceptual asymmetry that underpins the gray zone approach, Iran leverages a variety of operational, motivational, and temporal asymmetries. (For more on the various types of military asymmetries, see table 1 below.)

Table 1: Types of Military Asymmetries
Table 1: Types of Military Asymmetries
Table 1: Types of Military Asymmetries
Table 1: Types of Military Asymmetries
Table 1: Types of Military Asymmetries
Photo By: NDU
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Thus, Tehran has created a network of proxies that provide standoff, enable it to avoid becoming decisively engaged, and permit it to operate in a deniable fashion. The United States lacks a similar stable of proxies that it can rely on, so it must often act unilaterally. However, the tendency of the U.S. government to “leak” to the media and the desire of politicians to take credit for actions makes covert, deniable action difficult. Furthermore, a regional power like Iran that believes it is fighting for its survival will almost always be willing to assume greater risks than a distant great power that is not motivated by existential concerns and which has to tend to competing commitments around the world. Finally, while U.S. presidents must contend with public opinion and cannot assume they will have more than a single four-year term to accomplish their policy agenda, Iran’s key decisionmakers are unelected and therefore can often ignore public opinion when it comes to national security matters.7 And because they frequently have very long tenures, they can afford to be patient and play the long game. For instance, Ayatollah Khamenei has been Supreme Leader since 1989, while Qassem Soleimani had been the Islamic Revolution Guards Corps-Qods Force (IRGC-QF) commander since 1998, until he was killed in a U.S. drone strike in January 2020.

“U.S. presidents must contend with public opinion.” (Frank Hebbert, September 7, 2006
“U.S. presidents must contend with public opinion.” (Frank Hebbert, September 7, 2006
“U.S. presidents must contend with public opinion.” (Frank Hebbert, September 7, 2006
“U.S. presidents must contend with public opinion.” (Frank Hebbert, September 7, 2006
“U.S. presidents must contend with public opinion.” (Frank Hebbert, September 7, 2006
Photo By: Frank Hebbert
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On the operational and tactical levels, Iran leverages other types of asymmetries. It has exploited its geographic proximity to the Strait of Hormuz by creating naval forces capable of disrupting oil shipments from the region using small boat swarms (mass), mines and submarines (stealth), and drones and missiles (precision). It seeks to turn adversary strengths into vulnerabilities—for instance, developing anti-access and precision strike capabilities that can target U.S. carrier strike groups operating in the region’s waters and U.S. forces based around the rim of the Gulf.8 It also conducts actions that yield disproportionate effects, such as the October 1983 Marine Barracks bombing (with Lebanese Hezbollah), which forced U.S. peacekeeping forces out of Lebanon, and the drone and cruise missile strike on Saudi oil infrastructure in September 2019, which demonstrated Tehran’s ability to disrupt oil production in the region.


Most states possess hybrid military organizations, but hybrid actors like Iran put particular emphasis on employing regular and irregular forces together on the battlefield; blending conventional military capabilities, irregular tactics, terrorism, and criminal activities (for example, smuggling, money laundering, bribery, cybercrime, and illicit arms transfers); and conducting simultaneous operations across domains—land, sea, air, information, cyber, and space—to create synergies and maximize leverage. They do this to deter or coerce adversaries and influence or subvert foreign governments in order to achieve a desired political objective.9 Iran has created a complex institutional setup for projecting influence abroad consisting of both civilian and military entities, including the IRGC, IRGC-QF, IRGC intelligence, the Ministry of Intelligence and Security (MOIS); foreign Shi’ite proxy forces; the Ministry of Foreign Affairs (MFA); state media entities; and a variety of parastatal foundations and business fronts. This complexity derives in part from politics (and results in no small amount of friction among competing organizations) but it also facilitates the regime’s hybrid modus operandi.10 It does so by providing Iran with tools and options unavailable to its adversaries—such as terrorism and intimidation, bribery, and unbridled disinformation activities—which confer on it a comparative advantage when it comes to shaping the strategic environment and projecting influence below the threshold of war.

Deterrence: Linchpin of Iran’s Gray Zone Strategy

In the past four decades, Tehran has created a deterrence/warfighting triad consisting of (1) a guerrilla navy capable of disrupting oil exports from the Persian Gulf; (2) an arsenal of missiles and drones capable of conducting long-range precision strikes; and (3) a stable of foreign proxies—its Shi’ite foreign legion—capable of projecting influence throughout the region and acting as insurgents, counterinsurgents, and terrorists.11 It may now be adding a fourth leg to this triad; offensive cyber operations.12 These asymmetric capabilities enable Iran to deter by the threat of punishment—by imposing costs on its adversaries.

Iran is also building up its air defenses and hardening elements of its critical infrastructure (such as nuclear enrichment facilities) to deny its enemies the ability to destroy these potential targets.13 This enables it to deter by denial—by thwarting its adversaries’ aims.

Iran also relies on a variety of nonmilitary means to bolster deterrence—creating economic dependencies in neighboring states (for example, providing electricity to border provinces in Iraq), building external bases of support for Iranian policy among foreign Shi’ite communities, threatening to withdraw from arms control agreements (such as the 2015 nuclear deal and the 1968 Nuclear Nonproliferation Treaty),14 and frequent verbal warnings that a local clash could rapidly escalate and lead to “all-out war.”15 These steps strengthen Iran’s deterrent posture by fostering the belief that a conflict with the Islamic Republic could lead to another Middle East “forever war” and produce a highly destabilizing geopolitical mess.

Deterrence is the linchpin of Tehran’s gray zone strategy, as it constrains adversaries and thereby affords Iran greater freedom of action. And gray zone activities that showcase Iran’s precision strike, sea denial, and terrorist capabilities bolster its deterrent posture. In this way, Iran’s deterrent and gray zone activities reinforce each other.16

Iran’s Gray Zone Strategy: Core Elements

Iran’s gray zone strategy consists of a number of core elements: (1) tactical flexibility, strategic consistency; (2) indirection, ambiguity, and patience; (3) reciprocity, proportionality, and calibrated use of force; (4) protracting rather than escalating conflicts; (5) pacing and spacing activities; (6) diversifying and expanding options; and (7) dividing and encircling enemies. Each of these is addressed in greater detail below.

Tactical Flexibility, Strategic Consistency

Once Tehran commits to a particular strategic direction, deflecting it from its course is often difficult. It will probe and test limits, then back down (temporarily) if it encounters a firm response—renewing the challenge at another time and place, under more favorable circumstances. Conversely, the lack of a firm response frequently encourages more assertive behavior.17 Thus, Iran backed off from threats to close the Strait of Hormuz in January 2012 following new U.S. and EU sanctions, when Washington warned that doing so would cross an American redline.18 Yet when Washington suspended sanctions waivers on Tehran’s oil exports in May 2019 in an effort to drive Iranian oil exports to zero (crossing a longstanding Iranian redline—that if it cannot export oil, no Gulf state would export oil), Iran lashed out militarily, with attacks on Gulf oil transport and infrastructure.19 After the United States and its allies bolstered their maritime presence in the Gulf in response to these attacks, Iran then cautiously ratcheted up proxy rocket attacks in Iraq until an American was killed in December 2019.20

Indirection, Ambiguity, and Patience

Tehran often uses indirect means (for example, mines, IEDs, and rockets),21 foreign proxies (for example, Lebanon’s Hezbollah, Iraq’s Kata’ib Hezbollah, and to a lesser extent Yemen’s Houthis), and operations on foreign soil to create ambiguity, standoff, and to avoid decisive engagement with the enemy. It creates ambiguity to sow doubts about its role, encourage speculation about the culpability of rogue regime elements, and provide a face-saving “out” for conflict-averse adversaries. Because Iran prefers indirect action, and because it seeks advantage through incremental, cumulative gains, its approach requires patience. Moreover, Tehran’s preference for proxies seems at least partly rooted in a conspiratorial worldview in which ubiquitous enemies are perceived to be using proxies and agents against it, causing it to respond in kind.22

Reciprocity, Proportionality, and Calibrated Use of Force

Tehran generally uses force in a measured, tit-for-tat manner, responding in kind at a level broadly commensurate to the perceived challenge. It does so to garner legitimacy for its actions, to be more predictable—and to thereby limit the potential for miscalculation—and to deter. Thus, during the Iran-Iraq War, Iran responded to attacks on its oil industry with attacks on Gulf shipping; to air raids on Tehran with missile strikes on Baghdad; and to Iraqi chemical warfare by threatening chemical attacks of its own. From 2010 to 2012, Iran responded to cyberattacks on its nuclear program and oil industry, to financial sanctions, and to the killing of its nuclear scientists with cyberattacks on U.S. financial institutions and on Saudi Aramco, and by plotting attacks on Israeli diplomats in Georgia, India, Thailand, and elsewhere. Most recently, Iran responded to the Trump administration’s efforts to reduce its oil exports to zero with a limpet mine attack on four foreign oil tankers anchored off the Emirati coast, and to sanctions on its largest petrochemical company with a limpet mine attack on two foreign petrochemical tankers transiting the Strait of Hormuz.

Protracting Rather than Escalating Conflicts

Tehran’s preference for strategies of indirection and the calibrated (that is, limited) use of force ensures that conflicts it is involved in will often be protracted. This enables it to exploit the motivational asymmetries that it believes give it an edge in these long struggles, and to avoid escalation—which would generally play to its enemies’ strengths. Thus, in its decades-long struggle against U.S. influence in the Middle East, Tehran has supported proxy attacks on U.S. personnel and interests in order to wear down American resolve (for example, the 1983 U.S. Marine barracks bombing, the 1996 Khobar Towers bombing, and the provision of arms to Iraqi Shia insurgents fighting U.S. forces in Iraq from 2003 to 2011).

Tehran’s efforts to undermine Israel have likewise involved a patient, decades-long buildup of proxy and partner military capabilities in Lebanon (Hezbollah), Gaza (Hamas and Palestinian Islamic Jihad), and most recently Syria, where the IRGC-QF also conducts direct attacks on Israel—showing that Tehran will sometimes emerge from the gray zone to attack its enemies.23

Pacing and Spacing Activities

Tehran judiciously paces its activities—arranging them in time and space—to avoid creating an undue sense of urgency or an overstated perception of threat in the minds of foreign decisionmakers. It does this so that they will not overreact and so that events do not spin out of control. (The pacing of activities may also be influenced to some extent by the demands of consensus decisionmaking, military planning, and logistical considerations.) The pacing of activities may also reduce pressure on adversaries to act, and feed the hopes of some foreign decisionmakers that not responding militarily to Iranian actions will lead to de-escalation. Weeks or months may pass between Iranian activities in an ongoing gray zone campaign, or before Iran responds to an adversary’s actions. Thus, in Tehran’s counterpressure campaign against the Trump administration’s “maximum pressure” policy, it has conducted activities at varying intervals, along several lines of operation, in different domains, and diverse geographic arenas of operation (limpet mine attacks in the Gulf, rocket salvos in Iraq, drone and cruise-missile strikes in Saudi Arabia, and cyber operations against nearly all its adversaries).

Diversifying and Expanding Options

Tehran is an adaptive actor that adjusts its gray zone strategy as needed. To this end, it has developed a diversified toolkit to provide an array of both nonlethal and lethal options beyond vertical escalation, in both the physical and cyber domains, and in different arenas of conflict. This enables it to tailor its approach to adversaries and circumstances. (See table 2 for more about Iran’s gray zone toolkit.)

Table 2: Iran’s Gray Zone Toolkit
Table 2: Iran’s Gray Zone Toolkit
Table 2: Iran’s Gray Zone Toolkit
Table 2: Iran’s Gray Zone Toolkit
Table 2: Iran’s Gray Zone Toolkit
Photo By: NDU
VIRIN: 210319-D-BD104-004

Dividing and Encircling Enemies

Iran’s involvement in deniable/unacknowledged activities and its perceived willingness to escalate often stokes disagreements among policymakers in hostile states, tying the bureaucracies of these governments in knots. Thus, the June 1996 Khobar Towers bombing in Saudi Arabia sparked a bitter debate in the Clinton administration about how to respond.24 Likewise, Iran’s attacks in the Gulf from May to June 2019 intensified frictions between a war-averse President Donald Trump and his hawkish national security advisor, John Bolton, contributing eventually to the latter’s departure from government.25 Tehran likewise attempts to drive wedges within enemy coalitions. In response to the Trump administration’s maximum pressure policy, Tehran attacked and impounded tankers belonging to several U.S. allies, highlighting Washington’s unwillingness to defend them.

Finally, Tehran seeks to encircle adversaries with proxy or partner militaries. Hence Tehran’s support for Hezbollah in Lebanon and Hamas in Gaza, along with its efforts to create a Shi’ite militia army in Syria—to threaten Israel with a rain of destruction by rockets, missiles, and drones. Iran’s provision of missiles and drones used in Houthi attacks on Saudi Arabia and the United Arab Emirates (UAE) is driven by similar motives.

Lessons from Past U.S.-Iran Confrontations

Iran’s gray zone modus operandi, as well as its episodic involvement in overt military action, has been showcased in past periods of tension and confrontation between the United States and Iran. These include U.S. reflagging operations in the Gulf during the Iran-Iraq War; Iran’s lethal assistance to Shi’ite militant groups “resisting” the post–2003 U.S. occupation of Iraq; and the pressure/counter-pressure campaigns that preceded the 2015 nuclear deal with Iran (the Joint Comprehensive Plan of Action or JCPOA) and that followed the U.S. withdrawal from the JCPOA in 2018.

Gulf Reflagging Operations (1987–1988)

In response to Iranian small-boat attacks on neutral shipping during the latter phases of the Iran-Iraq War, the United States initiated Operation Earnest Will in July 1987 to escort reflagged Kuwaiti oil tankers in the Persian Gulf.26 With the start of operations, the Reagan administration warned Iran against attacking the convoys with Silkworm missiles as they transited the Strait of Hormuz. The administration assumed that the presence of the USS Kitty Hawk carrier battle group would deter Iranian countermoves.

While the launch of convoy operations caused Tehran to dramatically reduce its small-boat attacks, it was quick to indirectly challenge the United States: during the very first convoy, the tanker Bridgeton struck a covertly sown mine. Due to the limited damage, lack of casualties, and a desire to avoid escalation, the United States did not respond.

Within months, however, Tehran ramped up both its small-boat attacks and its mining operations. In September 1987, U.S. forces caught an Iranian ship, the Iran Ajr, laying mines in international waters; they scuttled the ship and detained the crew. The following month, Iranian forces launched two Silkworm missiles at a reflagged tanker in Kuwaiti waters, skirting the U.S. red line by conducting the attack far from the Strait of Hormuz. Perhaps to obscure their role, the attackers launched captured Iraqi Silkworms from the occupied al-Faw Peninsula. The United States responded by destroying two Iranian oil platforms used to support attacks; Iran retaliated with a Silkworm strike against Kuwaiti oil terminals, but instead hit a decoy barge.

As Tehran launched another mining operation in February 1988, Washington adopted more aggressive rules of engagement and tactics. Two months later, the destroyer USS Samuel B. Roberts struck a mine, spurring the Navy to destroy two more oil platforms used to support Iranian operations. In response, Iranian naval forces attacked several U.S. warships, which led the U.S. military to launch Operation Praying Mantis. During this action, the Navy sank an Iranian missile boat, frigate, and small boat; it also damaged a second frigate and several small boats, which fought on despite long odds. This marked the end of Iran’s mining operations, and with the ground war turning against it, attacks on shipping declined sharply for the duration of the fighting.

In July 1988, during one of these increasingly rare surface actions, the USS Vincennes accidentally downed an Iranian Airbus passenger jet, mistakenly believing it was a fighter jet. All 290 passengers aboard were killed, and Iran apparently believed it was an intentional act. The perception that the United States was entering the war on Iraq’s side helped convince Tehran to end the conflict.

In sum, Iran was not deterred by U.S. intervention, and American restraint further emboldened it. Tehran challenged the United States by indirect means (covertly sown minefields), circumvented U.S. red lines by launching missiles against reflagged ships no longer under escort, and ramped up attacks on unescorted ships that were not part of the reflagging operation. Tehran did not pull back until after Operation Praying Mantis, when its costs became prohibitive. Yet the U.S. intervention deterred direct attacks on convoys, forced Iran to rely on less effective tactics, and contributed to a diplomatic solution to the fighting, enabled by a series of devastating Iraqi victories on land.

Proxy Warfare Against U.S. Troops in Iraq (2003–2011)

During the U.S. occupation of Iraq, the IRGC-QF armed, trained, and financed Iraqi militias and insurgent groups that killed more than 600 U.S. troops. Tehran apparently hoped to tie down U.S. forces, dampen America’s appetite for further regional military adventures, and help its proxies eventually push the United States out of Iraq. With American forces ensconced next door and the stakes so high, Iran was willing to assume significant risk.27

For its part, Washington sought to disrupt Tehran’s efforts while avoiding escalation, so it generally acted with restraint. The U.S. military regularly interdicted Iranian arms shipments, and after sending a warning note that went unheeded, it launched a series of operations to detain senior Qods Force operatives; two in Baghdad (December 2006), five in Erbil (January 2007), and another in Sulaymaniyah (September 2007). A Hezbollah operative working for Iran was detained as well (July 2007). These detentions led Iran to seek direct talks with U.S. representatives in Baghdad (which were inconclusive) and caused the Qods Force to dramatically reduce its footprint in Iraq—though not to cease its activities there. The United States also privately threatened on several occasions to respond militarily to attacks by pro-Iran groups, including rocket attacks on the U.S. embassy in Baghdad in April 2008 and against several bases in Iraq in June 2011 (the latter attacks killed 15 U.S. soldiers). In both cases, attacks ceased after stern U.S. warnings.

Overall, Washington’s efforts to constrain Iran’s support for Iraqi proxies produced only modest results. The detention of Qods Forces operatives compelled Tehran to change its modus operandi and provided a brief impetus for renewed diplomacy. Quiet threats of a military response twice caused Iran to stand down. But U.S. actions ultimately failed to halt Tehran’s support for attacks on American forces or limit the growth of its influence in Iraq. Moreover, Tehran made no effort to hide its role: for example, the arms it shipped to militant Shia groups often retained the manufacturer’s logos and data plates. The standoff provided by proxy cutouts was apparently more important to Iran than deniability: the regime correctly calculated that the United States would not respond militarily to proxy operations even when Iranian sponsorship was evident.

Competing Pressure Campaigns (2010–2012)

In light of Iran’s continued nuclear activities in defiance of a half-dozen UN Security Council resolutions passed between 2006 and 2010, the United States, Israel, and the European Union started ratcheting up pressure to halt these activities via coercion and diplomacy.28 The United States and Israel, who had initiated a joint campaign of cyberattacks on Iran’s nuclear program starting in 2007, ramped up their activities, which continued through 2010. Israel killed a half-dozen Iranian nuclear scientists between 2010 and 2012 while threatening to launch a preventive strike against Iran’s nuclear infrastructure. The United States bolstered its forward military presence in the Gulf (maintaining a near-steady presence of two carrier strike groups in the region between 2010 and 2012) to deal with the potential fallout from an Israeli strike, and it intensified its drone operations over Iran and its periphery. Perhaps most importantly, Washington and the EU imposed harsh sanctions on Iran’s Central Bank and oil sector in 2011 and 2012.

Iran responded in kind while eschewing steps that could spark a broader conflict. It launched cyberattacks on U.S. financial institutions (2012–2013) and the oil giant Saudi Aramco (2012), plotted attacks on Israeli diplomats in retaliation for the killing of its scientists (2012), attempted to shoot down U.S. drones in the Gulf (2012–2013), and accelerated its nuclear program by increasing the number of operating centrifuges and its stockpiles of enriched uranium.

These dueling pressure campaigns became enmeshed with other covert campaigns, shadow wars, and overt conflicts that in many cases predated the nuclear crisis—including the Israel-Hezbollah conflict, the geopolitical rivalry between Saudi Arabia and Iran, and the Syrian civil war. The involvement of so many actors operating independently or in concert heightened the potential for crossover and inadvertent escalation. Tensions eventually abated because U.S.-EU sanctions had begun to bite and nuclear negotiations gained momentum. While covert action and military pressure campaigns slowed the nuclear program, it was sanctions that eventually brought Iran to the negotiating table, resulting in the conclusion of JCPOA in July 2015. Yet flaws in the nuclear accord contributed to the Trump administration’s May 2018 decision to leave the deal, paving the way for yet another pressure/counter-pressure campaign.

Countering U.S. Maximum Pressure (2019–2021)

In May 2018, President Trump announced that the United States would withdraw from the 2015 nuclear deal with Iran and instead pursue a policy of “maximum pressure.”29 The new policy sought to impose unbearable economic costs on Iran through sanctions, while deterring lethal attacks on U.S. personnel and interests.30 The ostensible goal of the new policy was to compel Tehran to abandon its malign activities and negotiate a new deal that would address a range of nuclear, regional, and military issues not dealt with in the JCPOA.31

Tehran initially responded with restraint, hoping that the European Union would ignore U.S. sanctions. When it became clear that this would not happen, and after Washington took additional steps to further intensify sanctions and collapse Iran’s economy, Tehran launched a counter-pressure campaign in May 2019 to compel the United States to ease or lift these sanctions and induce the rest of the world to ignore them.32

This counter-pressure campaign consisted of gray zone activities in multiple domains, along multiple lines of operation, and in diverse geographic arenas, including unacknowledged attacks on oil tankers in the Gulf and petrochemical infrastructure in Saudi Arabia; cyber operations; proxy attacks on U.S. personnel and facilities in Iraq; and incremental violations of JCPOA limits on its nuclear program.

Tehran graduated from simple to complex, and from nonlethal to lethal attacks against U.S. and allied interests in the region.33 Its initial attacks on oil transport and infrastructure, including limpet mine attacks on tankers in May and June of 2019 and a dramatic drone and cruise missile strike on Saudi oil infrastructure in September of that year, did not prompt the United States to ease sanctions or to respond militarily—except by bolstering its forward military presence in conjunction with several allied states (although the United States reportedly did respond to the shootdown of one of its drones in June with a cyberattack).34 These attacks by Iran, however, antagonized many countries dependent on Gulf oil, and they soon ceased. (Iranian naval forces also diverted a handful of foreign tankers in the Gulf as part of its counter-pressure campaign, though to little effect.)

Halting its attacks on Gulf oil, Iran then ramped up proxy rocket attacks in Iraq in November and December of 2019. This led to the death of an American contractor, prompting U.S. military strikes against Kata’ib Hizballah (KH) facilities in Iraq and Syria that killed 25 militiamen, and led to violent demonstrations in front of the U.S. embassy in Baghdad by pro-Iran proxies. This resulted in a U.S. drone strike on January 3 that killed IRGC-QF commander Qassem Soleimani and KH head Abu Mahdi al-Muhandis. Iran responded 5 days later by launching 16 missiles at al-Asad airbase in Iraq, producing no fatalities but giving concussions to more than 100 U.S. service members. Good intelligence and advance warning by Iran to Iraq that the attack was coming enabled U.S. personnel to shelter beforehand.35 Afterward, the United States and Iran signaled their desire to de-escalate, both publicly and via back channels.36

As Tehran pulled back, its Iraqi proxies ramped up rocket harassment attacks for several weeks thereafter—some of which were claimed by new, previously unknown groups to provide an added degree of standoff and deniability for Iran and its proxies. Another spike in proxy rocket attacks in March led to the death of three coalition soldiers (two Americans and one British) and another round of U.S. strikes on KH facilities in Iraq. Iran’s proxies ramped up rocket and IED attacks against U.S. embassy convoys in July–September 2020 before they dropped dramatically in October, presumably to avoid giving President Trump a pretext to hit Iran just prior to U.S. elections in November, when a U.S.-Iran clash might give the president a bump at the polls. Few rocket attacks occurred between October 2020 and the effective end of the U.S. “maximum pressure” policy, with the transfer of power to the administration of President Joe Biden in January 2021.

As part of its counter-pressure campaign, Tehran intensified cyber-spying and network reconnaissance activities—perhaps to pave the way for future attacks and to signal its ability to respond to a U.S. attack in the cyber or physical domain.37 It also continued ongoing cyber influence operations to discredit U.S. policy38 and launched operations to undermine the credibility of the 2020 U.S. presidential elections.39 And Iran repeatedly breached various JCPOA limits on its nuclear program, allowing it to accumulate quantities of low-enriched uranium sufficient (at the time of writing) for two bombs—if further enriched and weaponized.40

In sum, Tehran failed to compel Washington to ease or lift sanctions or to pull all of its troops out of Iraq and the Middle East.41 However, the lack of a U.S. response to a number of Iran’s actions in the Gulf and Iraq undermined America’s image as a steadfast and reliable partner, while the killing of Qassem Soleimani projected a reassuring image of resolve to some allies and an unnerving image of volatility to others.

It should be added that during this period, Iran continued to support its Yemeni Houthi allies in their ongoing war with the Saudi-led coalition, as well as its efforts to transform Syria into a springboard for military action against Israel. These parallel lines of operation each has its own distinct op tempo and logic, although Tehran has occasionally used the Houthis to convey threats to its Arab adversaries,42 while Israel is increasingly concerned about the possibility that Iran might encourage the Houthis to strike it.43

Moreover, Israel’s apparent sabotage of a centrifuge assembly facility at Natanz in July 202044 and the killing of Iran’s chief nuclear weapons scientist Mohsen Fakhrizadeh in November raised the question of Iranian retaliation against not only Israel, but possibly also the United States.45 The potential for spillover has heightened concerns about Washington’s ability to keep developments in these largely distinct arenas of conflict separate from the U.S.-Iran conflict. In the past, Tehran has treated these as separate tracks—seeking to avoid simultaneous escalation with the “little Satan” and the “great Satan.” Thus, it retaliated for the killing of its nuclear scientists from 2010–2012 by hitting only Israeli targets.46 It will likely continue to do so as long as the ever-cautious Ali Khamenei remains Supreme Leader.

Several conclusions can be drawn from these past showdowns:

  • Defining success in the gray zone: Conventional deterrence in the gray zone is challenging. Iran works assiduously to erode U.S. red lines or circumvent them, and to exploit asymmetries in motivation in order to advance its anti-status quo agenda. For this reason it is not possible for the United States to deter all of Iran’s malign activities. Success consists of deterring Iran from using its most potent capabilities, thereby forcing it to employ less effective means.
  • Iran shows strategic consistency, tactical flexibility: Tehran has relied on the same dog-eared playbook for nearly 40 years now. Tehran will frequently test or try to circumvent U.S. red lines, and while it may abandon a particular approach when faced with a firm response, it soon seeks alternative means of achieving its goals. It might relinquish those goals if they become too costly, but such a decision would depend on its assessment of Washington’s motivation, risk tolerance, and willingness to bear costs of its own. And it will sometimes use force to uphold its red lines.
  • Iran prefers indirection and ambiguity, but will act overtly when necessary: Although Tehran prefers indirection and ambiguity, its response to the targeted killing of Qassem Soleimani shows that it is willing to leave the gray zone and act overtly when red lines are crossed. This is not a departure from policy. For decades Tehran asserted that in response to an attack on its nuclear infrastructure, for instance, its missile arsenal would deliver a “crushing response” against its enemies. Overt action has always been part of Iran’s military repertoire.47 Embracing a gray zone strategy does not preclude overt, attributed activities, when it serves Iran’s interests.
  • The United States needs to respond more consistently and to strike a better balance between restraint and audacity: U.S. restraint and a lack of consistency in responding to tests and probes have often undermined U.S. credibility and invited additional challenges by Iran, leading to the very outcomes that policymakers had hoped to avoid. And exaggerated fears of escalation have often precluded American officials from effectively responding to Tehran’s actions. Yet, there are times when audacity can pay off: Operation Praying Mantis caused Iran to dramatically ramp down attacks on neutral shipping in the Gulf toward the end of the Iran-Iraq War, while the killing of Qassem Soleimani and Abu Mahdi al-Muhandis put Iran and its Iraqi proxies on their back heels, eliminated two talented, and perhaps irreplaceable, operators, and emboldened those in Iraq opposed to Iran and its influence there.48 On the other hand, prudence is sometimes in order: U.S. restraint following Iran’s retaliation for the killing of Qassem Soleimani helped de-escalate that situation.

(Hosein Charbaghi, January 6, 2020)
(Hosein Charbaghi, January 6, 2020)
(Hosein Charbaghi, January 6, 2020)
(Hosein Charbaghi, January 6, 2020)
(Hosein Charbaghi, January 6, 2020)
Photo By: Hosein Charbaghi
VIRIN: 210318-D-BD104-013

Toward a U.S. Gray Zone Strategy

The United States has had an uneven record of success vis-à-vis Tehran while employing conventional, overt military approaches. A U.S. gray zone strategy may therefore be a more effective way to counter Iran’s gray zone strategy. Such a strategy would turn Iran’s gray zone strategy against it, by posing for Tehran many of the dilemmas that its gray zone strategy has posed for Washington over the past 40 years. A U.S. gray zone strategy would rely on covert and unacknowledged activities to create ambiguity when responding to Iranian challenges. It would seek advantage by incremental gains to limit the potential for escalation. And it would employ discreet messaging to communicate red lines and when appropriate, to clarify intentions.49 Such an approach could limit Tehran’s freedom of action, avoid major escalation, and more effectively counter Iran’s efforts to alter the regional status quo—while creating space for diplomacy to reduce tensions. Doing so could alter the terms of engagement with Tehran by raising the costs of its current policy and forcing Iran to pursue its goals by less effective means.

A gray zone strategy would also be more sustainable—politically and militarily—than other recent U.S. military approaches to the region, as it would be more compatible with a number of American policy imperatives. These include;

  • Washington’s desire to restart negotiations with Tehran, as discreet covert or unacknowledged activities would be less likely to disrupt delicate diplomatic efforts than overt, demonstrative actions.
  • A strong bipartisan desire to avoid further escalation with Iran and more Middle Eastern “forever wars”—for the entire purpose of a gray zone strategy is to advance the national interest while avoiding escalation and war.
  • The need to operate in a manner better suited to the operational environment. A gray zone strategy would be more in sync with the political needs of regional partners (Iraq, Saudi Arabia, the UAE) and more consistent with the prerequisites for success in protracted conflicts that are won on “points” rather than through “knockout blows.”
  • The need to facilitate the ongoing shift of policy focus and military assets to the Indo-Pacific region (a policy pursued by both Democratic and Republican administrations), as a gray zone strategy in the Middle East could be accomplished with a relatively light force footprint.
  • The need to acquire competency in the conduct of gray zone activities in a new era of geopolitics that is likely to be increasingly “gray.”

Gray zone strategies can support very different policy objectives—defensive policies to deter and contain Iran or proactive policies that rely on initiated activities to impose costs on Iran and roll back its regional influence. Gray zone strategies can also be used to pursue mixed policy objectives: deterring and containing Iran in certain geographic regions and domains of military competition while pushing back against its activities and rolling back its influence in other arenas and domains.

To succeed in the gray zone, U.S. policymakers and planners will need to change the way they think, organize, and act. They must set aside the notion, which Tehran encourages, that a local clash could easily escalate to a major conventional war.50 The whole logic of Tehran’s gray zone strategy is to manage risk, avoid escalation, and prevent war. If U.S. policymakers understood this, it would immediately negate Tehran’s single most important advantage. Indeed, Israel’s covert operations in Iran and its activities since 2017 against Iranian forces in Syria have shown that it is possible to wage an effective gray zone campaign against Iran and its proxies without provoking a war.51

This means putting aside the vocabulary and mental models derived from America’s conventional warfighting experience and adopting alternative concepts more suited to activities below the threshold of war. This will not be easy, but it will be necessary if the United States is to succeed against Iran in the Middle East and against other gray zone actors like Russia and China.52 This also means abandoning certain ingrained habits of thought and action that are central to the American way of war but inimical to success in the gray zone, such as the preference for “decisive” force and the emphasis on lethality.53 Indeed, Iran’s ongoing counter-pressure campaign shows that even nonlethal gray zone activities can produce dramatic effects.54 In gray zone conflicts, less (lethality) may sometimes be more. Accordingly, the United States should diversify its policy toolkit to include more nonlethal anti-personnel and anti-materiel systems. Yet the potential for vertical escalation needs to remain part of the U.S. gray zone toolkit. Escalation dominance—embodied by America’s unmatched power-projection and precision-strike capabilities—constitutes one of its most potent asymmetric advantages vis-à-vis adversaries like Iran, and escalating in order to de-escalate may sometimes be necessary.

Greater consistency in responding to Iranian tests and probes and greater unpredictability in how the United States responds will also be critical to success. Policymakers and planners tend to focus on the mix of forward deployed capabilities needed to pose a credible threat to an adversary. But the credibility that Tehran assigns to forward-deployed forces is rooted in its assessment of America’s willingness to use them. Without credibility, all the carrier strike groups in the world will not deter Iran—as has been demonstrated on numerous past occasions. With credibility, the United States can keep fewer deployed assets in the Middle East; forces can be surged into the region during a crisis. Credibility cannot. And greater unpredictability in responding to challenges—by avoiding stereotyped responses and targeting assets that Tehran truly values—will complicate Iran’s risk calculus and likely induce greater caution in its behavior. When policymakers deem that a lack of predictability creates unacceptable risk, discreet back channel and public messaging can be used to reassure, clarify intentions, and de-escalate.

American policymakers and planners also have to consider the pacing and spacing of gray zone activities to reduce the potential for miscalculation and escalation. The old adage, “speed kills,” is especially apt here. What was often an asset in conventional operations is a liability in the gray zone. Impatient Americans must learn to embrace the deliberate pacing and spacing of gray zone activities and recognize that much of the “artistry” of strategy and operations in the gray zone resides in how these two elements are combined.

There is also a lesson here for those who fear that artificial intelligence will result in battles at hyperspeed and wars that spin out of the control of generals and policymakers.55 By limiting most military activities to set-piece gray zone operations that are properly paced and spaced, planners and strategists may ensure that in a future defined by the artificial intelligence revolution, technology and tactics will remain the servants of strategy and policy, and that humans will control events. The gray zone may well be the solution to dystopian fears of a loss of human control due to AI-driven hyperwar.

The U.S. government also needs to develop conceptual and institutional frameworks to enable it to design and implement interagency-led, multi-domain gray zone deterrence campaigns in which it can test, observe, learn, and adjust its gray zone strategy to determine what “works best.”56 And it needs to develop a gray zone strategy “with American characteristics” that will enable the United States to act quietly, patiently, and consistently below the threshold of war to deter adversaries, impose costs on enemies, and advance its interests.

Needless to say, such a U.S. gray zone strategy should reflect American values and build on existing U.S. capabilities. Thus, the United States would generally rely on unilateral covert or unacknowledged activities, as it lacks a stable of proxies like Iran does. Private military companies should generally not be used to fill such sensitive roles. Moreover, U.S. gray zone activities should, of course, be conducted in a manner compatible with the law of armed conflict and international law. This is key to building and maintaining broad international coalitions against actors like Iran that engender opposition from much of the international community because they regularly violate international laws and norms.57

Competencies existing mainly in the military’s special operations community and among CIA paramilitary forces (those parts of the U.S. government most comfortable thinking about and operating in the gray zone) will need to be cultivated and grown. And the tendency of politicians and officials to leak to the press and seek credit for military achievements, thereby complicating efforts to engage in covert/unacknowledged action, will need to be curbed.

America’s failure to adapt and operate effectively in the gray zone against an often struggling—albeit innovative and highly motivated—third-tier power like Iran, will raise questions about its ability to counter much more potent gray zone actors like Russia and China. And this will likely undermine U.S. deterrence not just in the Middle East but everywhere that it finds itself facing gray zone adversaries. So while the United States must continue to prepare for major conventional wars, it must also become adept in dealing with the “fifty shades of gray” that are likely to characterize future conflicts below the threshold of war, so that it may succeed in the strategic competitions of the future. PRISM

Michael Eisenstadt served for 26 years as an officer in the U.S. Army Reserve before retiring in 2010, serving on active duty at U.S. Central Command headquarters and in Turkey, Iraq, and Israel. His latest publication is Operating in the Gray Zone: Countering Iran’s Asymmetric Way of War from which parts of this article are drawn. He would like to thank Henry Mihm for his invaluable research assistance in preparing this paper, and three anonymous reviewers who provided helpful feedback on an earlier draft.


1 Lyle J. Morris et al., “Gaining Competitive Advantage in the Gray Zone: Response Options for Coercive Aggression Below the Threshold of Major War,” (Washington, DC: RAND, 2019), available at <>.

2 Arthur F. Lykke, “Defining Military Strategy: S = E + W + M,” Military Review (May 1989), 2–8. In addition, students of strategy have discussed the need to describe how the ways and means of strategy are combined in accordance with a guiding causal/strategic logic—a “theory of success”—to ensure that desired ends are achieved vis-à-vis a particular adversary. The theory of success is thus the “strategy bridge” that links ways and means to policy ends. It is constantly tested against reality, and modified in the course of conflict. For this reason, when properly practiced, strategy is essentially a learning process. See Frank G. Hoffman, “The Missing Element in Crafting National Strategy: A Theory of Success,” Joint Force Quarterly 97 (2nd Quarter), available at <>; Yossi Baidatz, “Strategy as a Learning Process: An Israeli Case Study for the New Administration,” Brookings Institution, Washington, DC, November 29, 2016, available at <>.

3 Michael J. Mazarr, Mastering the Gray Zone: Understanding a Changing Era of Conflict (Carlisle, PA: Army War College Strategic Studies Institute, December 2015), available at <>; David Barno and Nora Bensahel, “Fighting and Winning in the ‘Gray Zone,’” War on the Rocks, May 19, 2015, available at <>; and Philip Kapusta, “The Gray Zone,” Special Warfare (October–December 2015), available at <>.

4 Moosa Zargar et al., “Iranian Casualties During the Eight Years of the Iran-Iraq War,” Revista Saúde Pública (Brazil) 41, no. 6 (2007), 1065–1066, available at <>.

5 Michael Eisenstadt, “The Strategic Culture of the Islamic Republic of Iran: Religion, Expediency, and Soft Power in an Era of Disruptive Change,” Washington Institute for Near East Policy, Washington, DC, November 23, 2015, available at <>.

6 Department of Defense Cyber Strategy, Summary 2018 (Washington, DC: Department of Defense, 2018), available at <>; Zach Dorfman et al., “Exclusive: Secret Trump Order Gives CIA More Powers to Launch Cyberattacks,” Yahoo! News, July 15, 2020, available at <>.

7 Thus, just two months after Iranians engaged in widespread protests in December 2017 and January 2018 shouting slogans such as “Get out of Syria and take care of us,” the IRGC launched a drone strike against Israel from Syria, initiating a period of heightened tensions there. Several weeks after another round of protests occurred in November 2018 in response to a dramatic increase in gas prices, pro-Iran proxies ramped up rocket attacks on U.S. forces in Iraq, killing an American. And as the COVID-19 pandemic raged in Iran in early 2020, Iran continued efforts to build a military infrastructure in Syria to use as a springboard for attacks on Israel, and pro-Iran proxies in Iraq ramped up attacks on U.S. forces in Iraq, killing three coalition soldiers in March (two U.S. and one British). In all three cases, neither public opinion nor domestic circumstances seemed to affect Iran’s external behavior.

8 IRGC Commander Brig. Gen. Hossein Salami has described the logic behind Iran’s efforts to create ballistic missiles capable of targeting naval craft: “We were aware of the capabilities of the enemy’s naval strength, so we had to look for an asymmetric defense system against it . . . for example the enemy uses aircraft carrier [sic] and we could not build an aircraft carrier as it costs too much, so we decided to increase the precision of our ballistic missiles to confront the power of those aircraft carriers.” “Iran Considers Syria, Iraq as Its ‘Strategic Depth’: IRGC Deputy Cmdr.,” Mehr News Agency, February 4, 2018, available at <>. See also, “IRGC Commander Reiterates High Vulnerability of U.S. Aircraft Carriers,” Fars News Agency, April 28, 2012, available at <>.

9 This definition is based (with some alterations and additions) on Frank G. Hoffman, “Examining Complex Forms of Conflict: Gray Zone and Hybrid Challenges,” PRISM 7, no. 4 (2018), 37–38, 40, available at < well as the definition of hybrid warfare used by Hoffman in some of his earlier works>.

10 For more on these tensions and rivalries, see Tim Arango et al, “The Iran Cables: Secret Documents Show How Tehran Wields Power in Iraq,” New York Times, November 19, 2019, available at <>.

11 For more on how the various elements of Iran’s deterrence/warfighting triad fit together, see Michael Eisenstadt, “The Role of Missiles in Iran’s Military Strategy,” Policy Analysis, Research Note 39, Washington Institute for Near East Policy, Washington, DC, November 10, 2016, available at <>. See also Eisenstadt, “The Strategic Culture of the Islamic Republic of Iran.”

12 Michael Eisenstadt, “Iran’s Lengthening Cyber Shadow,” Policy Analysis, Research Note 34, Washington Institute for Near East Policy, Washington, DC, July 28, 2016, available at <>.

13 Farzin Nadimi, “Iran’s Passive Defense Organization: Another Target for Sanctions,” Policy Watch 3004, Washington, DC, Washington Institute for Near East Policy, August 16, 2018, available at <>.

14 Arsalan Shahla, “Iran Threatens Non-Proliferation Treaty Exit Over European Move,” Bloomberg, January 20, 2020.

15 Nasser Karimi and Jon Gambrell, “Advisor to Iran’s leader: US attack risks ‘full-fledged war,’” Associated Press (AP), November 19, 2020, available at <>; Tuqa Khalid, “Military strike against Iran would result in ‘all-out war’: Zarif,” Reuters, September 19, 2019, available at <>.

16 Michael Eisenstadt, “Operating in the Gray Zone: Countering Iran’s Asymmetric Way of War,” Policy Focus 162, The Washington Institute for Near East Policy, January 2020, available at <>.

17 Iran’s approach is reminiscent of the famous quote attributed to Vladimir Ilyich Lenin: “Probe with bayonets: if you find mush, push. If you find steel, withdraw.”

18 Kevin Hechtkopf, “Panetta: Iran Cannot Develop Nukes, Block Strait,” Face the Nation, January 8, 2012, available at <>; Elisabeth Bumiller, Eric Schmitt, and Thom Shanker, “U.S. Sends Top Iranian Leader a Warning on Strait Threat,” New York Times, January 12, 2012.

19 Babak Dehghanpisheh, “If Iran can’t export oil from Gulf, no other country can, Iran’s president says,” Reuters, December 4, 2018, available at <>.

20 It did so even though Washington had warned Tehran that the killing of an American was a redline. Missy Ryan, Greg Jaffe, and John Hudson, “Pompeo Warns Iran About Trigger for U.S. Military Action as Some in Administration Question Aggressive Policy,” Washington Post, June 18, 2019, available at <>.

21 The use of mines, IEDs, and rockets is considered a form of “indirect” action here because they provide a degree of standoff, and enable the belligerent to avoid decisive engagement with the enemy.

22 This is also a feature of Iran’s domestic politics, which has often seen the use of shadowy paramilitary-type groups such as Ansar-e Hezbollah to attack reformist politicians who are perceived as threats to “the system.” This would seem to indicate that these are culturally patterned approaches to domestic politics and foreign policy. For more on conspiracies and Iranian politics, see Ervand Abrahamian, “The Paranoid Style in Iranian Politics,” in Khomeinism: Essays on the Islamic Republic (Los Angeles: University of California Press, 1993), 111–131, and Ahmed Ashraf, “Conspiracy Theories,” Encyclopedia Iranica, December 15, 1992, available at <>.

23 Israel says Iran drone downed in Feb was on attack mission,” AP, April 13, 2018, available at <>.

24 Louis J. Freeh, “Khobar Towers,” Wall Street Journal, June 23, 2006, available at <>.

25 Jennifer Jacobs et al., “Trump Discussed Easing Iran Sanctions, Prompting Bolton Pushback,” Bloomberg, September 11, 2019. 9

26 This section draws heavily on David Crist, The Twilight War: The Secret History of America’s Thirty Year Conflict with Iran (New York: Penguin Press, 2012); Gregory F. Giles, “Deterring a Nuclear-Armed Iran from Adventurism and Nuclear Use,” in Tailored Deterrence: Influencing States and Groups of Concern, eds. Barry Schneider and Patrick Ellis (Maxwell AFB: USAF Counterproliferation Center, 2011), 1–36; and David Crist, “Gulf of Conflict: A History of U.S.-Iranian Confrontation at Sea,” Policy Focus 95, The Washington Institute for Near East Policy Washington, DC, June 2009, available at <>.

27 This section draws heavily on Crist, The Twilight War and Giles, “Deterring a Nuclear-Armed Iran from Adventurism and Nuclear Use,” 1–36.

28 This section draws heavily on Michael Eisenstadt, “Not by Sanctions Alone: Using Military and Other Means to Bolster Nuclear Diplomacy with Iran,” Strategic Report 13, Washington Institute for Near East Policy, Washington, DC, July 2013, available at <>.

29 This section draws heavily on Michael Eisenstadt, Deterring Iran in the Gray Zone: Insights from Four Decades of Conflict, The Washington Institute for Near East Policy, Washington, DC, forthcoming.

30 Missy Ryan, Greg Jaffe, and John Hudson, “Pompeo Warns Iran About Trigger for U.S. Military Action as Some in Administration Question Aggressive Policy,” Washington Post, June 18, 2019, available at <>; Joe Gould, “CIA Director Confirms He Sent Warning Letter to Iranian Quds Commander,” Defense News, December 2, 2017, available at <>.

31 Michael R. Pompeo, “After the Deal: A New Iran Strategy,” speech, U.S. Department of State, May 21, 2018, available at <>.

32 In April 2019, Washington announced that it would cease issuing sanctions waivers for eight countries that imported oil from Iran, to drive Tehran’s oil exports—once the largest source of government revenue—to zero. Michael R. Pompeo, “Decision on Imports of Iranian Oil,” press statement, U.S. Department of State, April 22, 2019, <>.

33 Thus, Iran’s first attack on oil transport in May 2019 was a simple limpet mine attack against oil tankers parked in an anchorage, while its second in June was a more complex limpet mine attack against tankers underway near the Strait of Hormuz. Its first attack on infrastructure in May was a simple drone attack on the Saudi East-West oil pipeline, and its second in September 2019 was a complex drone and cruise missile strike on two separate locations in Saudi Arabia.

34 Ellen Nakashima, “Trump approved cyber-strikes against Iranian computer database used to plan attacks on oil tankers,” Washington Post, June 22, 2019, available at <>.

35 Kamal Ayash and Mark Davison, “Hours of Forewarning Saved U.S., Iraqi Lives From Iran’s Missile Attack,” Reuters, January 13, 2020, available at <>; Qassim Abdul-Zahra and Ali Abdul-Hassan, “US Troops in Iraq Got Warning Hours Before Iranian Attack,” AP, January 13, 2020, available at <>. See also Mark Mazzetti et al., “3 Hours from Alerts to Attacks: Inside the Race to Protect U.S. Forces from Iran Strikes,” New York Times, January 8, 2020.

36 Nicole Gaouette et al., “Trump Says ‘Iran Appears to be Standing Down’ Following its Retaliatory Attacks Against Iraqi Bases Housing U.S. Troops,” CNN, January 8, 2020, available at <>; Drew Hinshaw, Joe Parkinson, and Benoit Faucon, “Swiss Back Channel Helped Defuse U.S.-Iran Crisis,” Wall Street Journal, January 10, 2020, available at <>.

37 CISA Statement on Iranian Cybersecurity Threats, June 22, 2019, available at <>. See also Thomas S. Warrick, “If the US launches cyberattacks on Iran, retaliation could be a surprise,” Fifth Domain, January 30, 2020, available at <>.

38 Emerson T. Brooking and Suzanne Kianpour, “Iranian Digital Influence Efforts: Guerilla Broadcasting for the Twenty-First Century,” The Atlantic Council, February 11, 2020, available at <>.

39 Ellen Nakashima et al., “U.S. government concludes Iran was behind threatening emails sent to Democrats,” Washington Post, October 22, 2020, available at <>.

40 David Albright, Sarah Burkhard, and Andrea Stricker, “Analysis of November 2020 IAEA Iran Verification and Monitoring Report,” Institute for Science and International Security, Washington, DC, November 12, 2020.

41 Remarks by President Trump in Cabinet Meeting, October 21, 2019, available at <>.

42 Paul D. Shinkman, “Iran issues veiled threat to UAE of attacks similar to Saudi oil strikes,” US News & World Report, September 17, 2019, available at <>.

43 Judah Ari Gross, “IDF Deploys Air Defenses to South Amid Threats of Attack From Yemen,” January 7, 2021, available at <>.

44 Farnaz Fassihi, Richard Pérez-Peña, and Ronen Bergman, “Iran Admits Serious Damage to Natanz Nuclear Site, Setting Back Program,” New York Times, July 5, 2020.

45 Michael Eisenstadt, “How Might Iran Respond to Foreign Sabotage?” PolicyWatch 3359, Washington Institute for Near East Policy, Washington, DC, August 4, 2020, available at <>.

46 Joel Greenberg, “Israel Says Thai Bombs Similar to Those in India, Georgia,” Washington Post, February 16, 2012, available at <>.

47 “Deputy Top Commander: Crushing Response Waiting for US Military Threats Against Iran,” Fars News Agency, July 3, 2015; Marcus George and Zahra Hosseinian, “Iran Will Destroy Israeli Cities if Attacked: Khamenei,” Reuters, March 21, 2013, available <>; “Commander: IRGC Will Destroy 35 US Bases in Region if Attacked,” Fars News Agency, July 4, 2012.

48 John Davison and Ahmed Rashid, “Iran Changes Tack in Iraqi Politics After Mastermind’s Assassination,” Reuters, May 27, 2020, available at <>; Qassim Abdul-Zahra and Samya Kullab, “Troubled Iran struggles to maintain sway over Iraq militias,”AP, June 11, 2020, available at <>.

49 For more on what an American gray zone strategy against Iran might look like, see Eisenstadt, “Operating in the Gray Zone, 26–38. See also Eisenstadt, “Deterring Iran in the Gray Zone: Insights from Four Decades of Conflict” The Washington Institute for Near East Policy, Washington, DC, forthcoming.

50 Nasser Karimi and Jon Gambrell, “Advisor to Iran’s leader: US attack risks ‘full-fledged war,’” AP, November 19, 2020, available at <>; Tuqa Khalid, “Military strike against Iran would result in ‘all-out war’: Zarif,” Reuters, September 19, 2019, available at <>.

51 “Iran Military Insists Only Eight Servicemen Killed in All Israeli Raids in Syria,” Radio Farda, July 17, 2020, available at <>.

52 Lyle J. Morris et al., Gaining Competitive Advantage in the Gray Zone: Response Options for Coercive Aggression Below the Threshold of Major War (Washington, DC: RAND, 2019), available at <>.

53 Summary of the 2018 National Defense Strategy (Washington, DC: Department of Defense, 2018), 4, 5, 6, 7, 10, available at <>.

54 According to one report, Supreme Leader Ali Khamenei approved the September 2019 attack on Saudi oil infrastructure on the condition that no civilians or Americans be killed. Michael Georgy, “‘Time to Take Out Our Swords’: Inside Iran’s Plot to Attack Saudi Arabia,” Reuters, November 25, 2019, available at <>.

55 Amir Hussein and John Allen, Hyperwar: Conflict and Competition in the AI Century, (Austin, TX: Spark Cognition Press, 2018). See also, Paul Scharre, “A Million Mistakes a Second,” Foreign Policy, September 12, 2018, available at <>.

56 For more on deterrence campaigns, see Kevin Chilton and Greg Weaver, “Waging Deterrence in the Twenty-First Century,” Strategic Studies Quarterly 3, no. 1 (Spring 2009), 34–35. See also Moni Chorev, “Deterrence Campaigns: Lessons from IDF Operations in Gaza,” Begin-Sadat Center for Strategic Studies, Middle East Security and Policy Studies no. 115, March 2016, available at <>.

57 Morris, Gaining Competitive Advantage in the Gray Zone, 133–136.