Key Point: Global shipping is vulnerable to Iranian deterrence.

The recent mining of two oil tankers in the Gulf of Oman, attributed to Iran by the United States, offers an important window into the strategic thinking of Iran and similarly situated regional powers. The incident is notable because the act of mining a limited number of vessels makes relatively little sense when viewed through the lens of traditional patterns of coercive behavior. Limited coercive acts typically have little value with regards to gaining concessions from a determined opponent. Generally, these acts may serve as a visible demonstration of a state’s willingness to enact some other, more substantial threat, such as shutting down the Strait of Hormuz outright. However, this requires the state making the threat to have the capacity to make good on its more substantial threats and for its opponents to believe that it is willing to incur the risks entailed. Iran, however, could not shut down the Strait of Hormuz for very long even if it wished to—something noted by President Donald Trump—and is unlikely to incur the substantial risks that an attempt would entail. Iran’s opponents, then, clearly don’t see its limited provocations as harbingers of something worse.

If Iran cannot shut down the Strait of Hormuz, or convince either the United States or its regional allies such as Saudi Arabia that it can do so, then it becomes attendant to ask what the value of limited coercive acts is. One argument goes that limited actions can achieve disruption and price spikes with regards to oil irrespective of whether Iran can shut down the Strait o Hormuz. However, it is unclear how this would help coerce either the United States or Iran’s regional adversaries. Driving up the price of oil globally does not hurt regional countries, which rank among the world’s major oil producers, and will likely have mixed effects on the economic health of the United States, which is an increasingly large player in the energy market. To the extent that limited attacks could serve a coercive role, it would be as costly signals of Iran’s willingness to shut down the Strait of Hormuz entirely—something that would have a major effect on regional powers which rely on the straits for up to 90 percent of their imports and exports. Given that Iran’s ability to sustain such an operation is limited, however, and given that shutting down the Strait of Hormuz entirely entails unacceptable escalatory risks , it is unclear why decisionmakers in Tehran would expect their counterparts in Riyadh or Washington to treat the threat to do so as being credible irrespective of Iran’s limited provocations. Even if leaders worry that they might have miscalculated Tehran’s intentions, the fact remains that Iran’s capabilities cannot sustain the closure of the Strait of Hormuz for a prolonged period of time. To make this threat credible then, Iran’s likely opponents would have to believe that Iran would risk heavy retaliation, the possible dismantlement of IRGCN facilities at Abu Musa and Farsi and a postwar settlement which would almost certainly be negative in order to create a temporary closure of the Strait of Hormuz.

A window into Iran’s strategic calculus, however, might be provided by way of an analogy with nuclear strategy. Scholars and practitioners have long puzzled why states would seek to maintain breakout capabilities. Easy to destroy and risky to produce, these very limited capabilities provide virtually no deterrent against a well-armed adversary. The possession of nuclear breakout capabilities makes sense, however, in the context of what Vipin Narang dubs a catalytic strategy. The target audience of a catalytic strategy is one’s partners not one’s adversary. By threatening to make a situation more volatile in a way that might endanger some of a larger partner’s interests a smaller state can secure support and concessions from its larger partners. Thus, for example, several of America’s Cold War partners maintained nuclear breakout capabilities because threat they posed to the U.S. nonproliferation agenda served to ensure sustained American support. This was because American policymakers calculated that security concessions to allies would prevent them from taking more radical steps to ensure their own security such as nuclear breakout.

Today, Iran is pursuing a catalytic strategy vis-a-vis the European states which, at least with regards to a shared desire to retain the JCPOA, are its partners. The strategy is proceeding on two fronts—the looming threat of Iran breaking out of the JCPOAs limitations on its nuclear program and a campaign to highlight Iran’s ability to generate spikes in the price of oil which would affect the European Union twenty-eight to a far greater degree than either the United States or Iran’s regional rivals. It is, then, perhaps no surprise that the surge in Iranian provocations coincided with ongoing negotiations with European partners regarding mechanisms for sanctions relief such as the INSTEX payment mechanism by which European companies can conduct non-dollar trade with Iran. While limited coercion in the gulf cannot improve Iran’s position vis-a-vis its adversaries, it can improve its bargaining position vis-a-vis countries which find themselves with congruent policy interests with regards to the U.S. policy of maximal pressure. Given Iranian policymakers recent complaints regarding the ineffectiveness of European initiatives, this is likely a means of signaling Iran’s European counterparts that they need to offer substantive support to Iran’s economy or risk Iran taking steps in the gulf that jeopardize their interests.

The Limited Risk of Iran Closing Hormuz

While the Iranian Navy and IRGC(N) retain the capabilities to, on paper, substantially disrupt transit through the Strait of Hormuz, a scenario specific analysis illustrates that the ability of Iran to accomplish this end is overstated. Take, for example, Iran’s significant stockpile of around five thousand naval mines. To close the Strait of Hormuz, the Iranians would have to emplace at least one thousand such mines across the twenty-five kilometers strait unobserved. The IRINs Kilo class submarines, which are twenty-five meters from the keel, would struggle to navigate these waters. Alternatively, Iranian forces could rely on the IRGCNs fleet of small boats or requisitioned civilian vessels to accomplish this end but would struggle to avoid detection if it mustered the number of vessels needed to do this in a short time span. Moreover, given that usable shipping channels span around 20 percent of the strait’s width, this would entail a modest concentration of around two hundred mines per channel. To open the straits for shipping in the short term, the United States and its allies would need to open one or more shipping channels, not clear every Iranian mine in the area.

Iran could attempt to disrupt minesweeping efforts with anti-ship missiles like the Chinese C-802 launched from shore-based launchers or the IRGCNs fleet of guided missile boats. However, firing missiles requires targeting data from vulnerable shore-based radar—which will likely be hit early in a conflict scenario. Moreover, the particularities of the Gulf operating environment do not favor missile salvos. Cruise missiles guided by heat and infrared seekers that rely on differentials between an object’s heat emissions and the background temperature would have their operations confounded by gulf climatic conditions and would struggle to approach targets such as mine clearing vessels or civilian vessels, which do not emit a distinctive heat signature. Radar-guided missiles would also lose effectiveness amid the cluttered environment of the Gulf, which is characterized by features such as islets and oil rigs all of which have a radar cross section sufficiently large to divert a missile. Kinetic and non-kinetic missile defense by U.S. destroyers in the form of jamming radars, spoofing seekers and shooting down missile salvos would further degrade the effectiveness of cruise missile salvos. Perhaps most notably, however, the islands which house the IRGCNs fast-attack craft would likely come under sustained air assault and perhaps occupation. During Operation Earnest Will, for example, the U.S. Navy considered the bombardment and occupation of Abu Musa and Farsi Island as a means of cutting off the IRGCNs fast-attack craft. As such, launching salvos of potentially ineffective cruise missiles entails uncertain benefits and substantial risks with regards to the expansion of the war to Iranian soil.

One might argue that Iran does not need to shut down the flow of oil through the Gulf completely—merely destroy enough ships for commercial companies to avoid the straits or insurance companies to raise premiums to levels inimical to commerce. However, if historical precedent is anything to go by, even sustained attrition of commercial vessels may not accomplish this. During the Iran-Iraq tanker war, for example, traffic through the Gulf continued partially because shipping companies higher premiums were offset by could charge customers higher rates on delivery as prices came to factor in the risks undertaken. This, moreover, was the case in a scenario where both parties were able to impose significant costs on the others shipping for a protracted period—something unlikely to be the case if Iran tries to close the Strait of Hormuz today.

As such, demonstrations of force in the straits have little utility for Iran vis-a-vis either the United States or Gulf states. A limited act of coercion typically only makes sense as a signal of one’s willingness to take an even more escalatory step if pushed further. Given just how poorly placed Iran is to make good on such a threat regardless of its intentions, it is unclear that limited coercive steps serve this role.