Tensions are escalating with the Islamic Republic of Iran. On May 12, a flurry of press reporting claimed that four oil tankers – two of which were operating under a Saudi flag – were subject to “sabotage” near a major international waterway. In the aftermath of the incident, unnamed American officials told the press that this was the work of Tehran or its proxies, while others went on record to clarify US-Iran policy. Reporting by CBS News as of May 15 reveals that US Secretary of State Mike Pompeo believes that Washington will know the answer to who was directly responsible for the attacks “in the coming hours and days.”

Where did the attack happen and to whom?

The attacks allegedly took place near the western edge of the Gulf of Oman close to the port city of Fujairah, in the United Arab Emirates. Fujairah lies south of the Strait of Hormuz, which is a major international transit route for oil tankers and commercial ships traveling to and from the Persian Gulf. The four tankers reportedly targeted were operating under the flags of Saudi Arabia (Amjad, Al Marzoqah), the United Arab Emirates (A.Michel), and Norway (Andrea Victory). Images circulating in the press as evidence of the attack almost exclusively showed the Andrea Victory, which had a hole blown into its hull where it meets the waterline. According to military investigators that spoke to the AP, there were holes in each vessel, each of which were reportedly “5- to 10” feet. The Drive has reported that despite a statement from Saudi officials about “significant” damage, there is no photographic evidence of the alleged wreckage on the two Saudi tankers – only one of which was reportedly carrying oil.

What sort of attack took place?

Reportedly, pro-Iran outlets had been the first to claim that there had been several explosions in the port of Fujairah last Sunday. While those reports were later disproven, select Iranian officials, such as the Chairman of the Parliament’s National Security and Foreign Policy Commission, used reporting about the explosions to say “the security of the south of the Persian Gulf” was akin to “glass.” The cryptic nature of the reporting last Sunday, even in English among the Western press, which continued to reference the notion of “sabotage” or an “attack” on the tankers without any clear details or descriptions, added to the confusion.

Through process of elimination, it is possible to narrow down the sort of attack on the Andrea Victory (in the high-likelihood that it came from Iran or an Iran-backed proxy group) given what is known about Tehran’s strategies, capabilities, and intentions, as well as assistance from open-source reporting as the story developed. This process of elimination leads to and seconds the conclusion that independent analysts and unnamed US authorities have more recently put forth: that “mines” were used, likely by a team of Iranian military divers.

First, even without seeing any images of the damage done to the hull of the Andrea Victory, it would be highly unlikely for the regime, or any of its proxies, to have fired a missile, be it an anti-ship cruise missile (ASCM) or an anti-ship ballistic missile (ASBM) from Iranian territory against these vessels. While Iran does have an arsenal of ASCMs (many of which are copies or variants of Chinese-supplied ASCMs) and ASBMs (which are variants of an Iranian single-stage solid-fuel short-range ballistic missile called the Fateh-110), such a launch would be inconsistent with Iran’s more graduated approach to escalation. It would also clearly feature a return address for those who would want to retaliate against the regime for such a crass and overt attack on a civilian vessel. Reading in a picture of the damaged hull of the Andrea Victory would also eliminate this option given that even Iran’s shorter-range projectiles (as used in older military drills) carry a high-explosive warhead that would likely leave a larger hole.

Next, while plausible only due to the reference to “explosive charges” in an article from the AP as well as unclear imagery initially making it hard to deduce if the metal in the hull was blown-in or blown-out, was the possibility of a bomb being planted aboard the vessel. But for this to be true, it would have to mean that where the hull was ripped apart (where the waterline is) would have to be accessible from inside the vessel, which is likely not possible. Moreover, the level of coordination required and chances of being caught would be significantly greater in this instance, making it harder to pull-off in less time.

Ruling out missiles launched from the Iranian coastline and hand-placed explosives, and coupling that with more clear imagery of the Andrea Victory, some sort of rocket-propelled grenade (RPG) attack could be possible, but not the most convincing. It would be difficult to imagine that Iran or an Iran-backed proxy could fire an RPG right at the waterline of the hull, as well as get away with no public reporting about sighting these fast-attack craft.

This leaves a tried and tested weapon for Iran: naval mining. Iran previously engaged in mining operations in the Persian Gulf as one way to impede the shipping of select Gulf States such as Kuwait and Saudi Arabia, which stood with Iraq during the Iran-Iraq War in the 1980s. Iran’s proficiency for using naval mines has grown over the years, as has the country’s mine inventory. Both Iran’s Fateh-class submarine and Ghadir-class mini submarine have the capability to carry and lay mines. Given what has been reported about these mines sticking to the hull of the vessel, an operation to stick the mines to hulls of the vessels by Iranian or pro-Iran divers seems more likely, but also raises new questions about the diver subset of Tehran’s marine capabilities.

Why does the timing matter and why would Iran (or any Iran-backed force) do this?

The attacks on the vessels follow an intensification of US pressure on Iran, particularly in the month of April. Last month, the Trump administration took several historic steps such as terminating all oil sanctions waivers and formally designating Iran’s Islamic Revolutionary Guard Corps (IRGC ) a Foreign Terrorist Organization (FTO). These moves, coupled with the aggregate economic pain caused by the restoration of sanctions over the past year may have incentivized Tehran to take a different approach (graduated escalation as opposed to strategic patience) to Washington’s “maximum pressure” policy as it enters year two.

In the run-up to May 8 (the one-year anniversary of when the US left the Iran nuclear deal and commenced its economic pressure campaign), US officials used the bully pulpit to relay that America was growing its military assets in the Persian Gulf in response to new threats from Iran or Iran-backed groups. While it was later revealed that part of the US military deployment was already scheduled, and that some of the deployment made up for deficiencies in US force posture in the region in 2018 (relating to carriers and missile defense), the message was clear: America was very publicly beefing-up its deterrence against Iran and citing problematic Iranian behavior as the reason.

On May 8, as Washington announced increased penalties on Iran – this time on the regime’s industrial metals trade – Tehran signaled that it would be incrementally limiting its adherence to the nuclear deal under two sixty-day windows (The second of those timetables, starting on July 7/8 – should Tehran follow-through on its own threats – would essentially put the Islamic Republic in material breach of the deal). The next day on May 9, the US Maritime Administration gave notice of increased threats to vessels operating in the Persian Gulf. Only three days later, on May 12, attacks were reported on oil tankers just southeast of the Persian Gulf.

And while formal and official attribution is still pending, the attack has all the hallmarks of an Iranian or Iranian-backed attack. It is asymmetric, it is deniable, it is below the threshold for the use of force to respond to (aka it is consistent with Iran’s proficiency in “gray zone” warfare), it is a type of activity that Iran has engaged in before, the target is a clear adversary of the Islamic Republic, and the move is intensely symbolic. There is also a clear historical and strategic parallel in another domain of warfare: Iran’s use of Improvised Explosive Devices (IEDs) and Explosively Formed Penetrators (EFPs) against the US and coalition forces in Iraq. A US military official presciently drew this reference to Iranian mining capabilities in 2012, saying, “We’ve been there before, we just called it an IED.” Iran’s return to mining can be interpreted as exporting its successful method of low-intensity warfighting and terrorism to the sea.

Should Iran have taken the decision to attack civilian vessels that carry oil, it could represent one way to do damage to global oil shipments without having to shut down all traffic in the Strait of Hormuz. Such a move is consistent with Iran’s highly graduated approach to escalation, which features raising costs to an adversary over time, signaling room to escalate further if its demands are not met, all the meanwhile seeking to avoid a direct confrontation. Moreover, given the aforementioned political timeline, the attack could be seen as complementing – in a covert fashion and in a different domain – the timetable for overt escalation in the nuclear domain during year two of maximum pressure.

A US policy puzzle?

Members of the Trump administration have promised to hold the Islamic Republic accountable for the actions of its proxies. Indeed, on May 13, US Special Representative for Iran Brian Hook, stated, “Tehran will be held accountable for the attacks of its proxies.”

However, there is a strong bipartisan track record of foreign policy failures on Iran to do exactly that. Even when administrations, including the current one, do seek to hold Iran accountable for the behavior of its proxies, the cost of acting on this principle has induced restraint and retreat, which in turn risks signaling irresolution. Indeed, after attacks against American military and diplomatic installations in Iraq in September 2018, the administration promised to hold Iran accountable for the actions of its proxies. However, it instead closed the Consulate in Basra. More recently, on May 15, it was reported that Washington was evacuating all non-essential personnel from the US Embassy in Baghdad. According to a Wall Street Journal reporter who previously led the bureau in Baghdad, the US did not take these steps even as attacks occurred on a daily basis against the “green zone” where America’s diplomatic facilities were located.

Why does the Persian Gulf (and by extension the maritime domain) matter?

Beyond commonplace invocations about energy security, oil prices and oil market stability, or even freedom of navigation and defense of the global commons, the Persian Gulf matters for US national security because it is one of several “contested domains” with the potential for escalation – be it intentional or accidental – between Tehran and Washington.

It is here, and in associated maritime environments like the Strait of Hormuz and Gulf of Oman (and increasingly even the Red Sea), that inferences about American resolve have been and will continue to be made by Iran. These inferences, along with the rest of Washington’s military posture and rhetoric, will be used to calibrate responses by Tehran to the maximum pressure campaign, as well to cease or continue testing America. Should Iran sense weakness, confusion, irresolution, or worse, no sense of strategy underwriting America’s escalating sanctions, the regime will likely lash out to signal that it too, has options and will act to defend its core interests. Rather than run away from an escalatory spiral that it cannot win, Iran could read American irresolution as an invitation to take greater risks.

Iran’s risk-tolerant IRGC Navy (IRGC-N) has operational authority in the Persian Gulf. Previous Worldwide Threat Assessments from the US intelligence community in 2018 and 2019 paint a picture of this force’s diminishing will to test the US – at least via fast attack craft. To explain the diminishing number of harassment attacks of US vessels by Iranian speedboats, hardline Iranian media outlets like Defa Press have woven together the fictional narrative that it is America, not Iran, which has adjusted its behavior in the Persian Gulf – citing the regime kidnapping of American sailors in 2016 as the reason.

But over the past two years, Iranian tactics have been evolving in the Persian Gulf. Iran is now a drone power, and much like other theaters of competition, it has taken to using drones to test its adversaries. In the Persian Gulf, Iran has used drones to buzz, harass, and monitor American vessels, thus beginning to change its traditional method of engagement from manned to unmanned. However, while Washington should worry about drones replacing speedboats in this arena, Iran continues to misrepresent its willingness to challenge the US to its own population. This was most recently evidenced by footage that was supposed to have been taken by an Iranian drone filming an American vessel in April, but really was a patchwork of old pictures and film.

To be clear, the US and Iran have come to blows in the Persian Gulf in the past. During the Iran-Iraq War, the US Navy sunk several Iranian vessels and oil platforms in response to Iran’s harassment of shipping and mining of waterways. But despite scoring decisive victories decades ago, Washington continues to live with the ghosts of that conflict, one of which is Iran’s continued threats to close the Strait of Hormuz. Both during the war as well as now, the ultimate political goal driving Iranian behavior towards America in the Persian Gulf has been the same: to create an unsafe maritime environment that forces America out of the region and provides Iran with a vacuum to fill and the opportunity to exert hegemony.

It is in this vein that Iranian use of mines against civilian vessels matters most: as an act of terrorism designed to signal resolve and risk tolerance as part of the regime’s larger competition against America.

Late in the Iran-Iraq War in 1987, the CIA reported that, “Terrorism is an important instrument of Iranian foreign policy… Tehran has never been made to pay a significant price for the use of terrorist tactics as a political weapon, a factor that reinforces its willingness to use them.” If the US genuinely wants to see Iran come back to the negotiating table, it cannot afford to swerve in the face of the first threat, be it in the maritime or nuclear domains by the Ayatollahs. If it is intimidated by such actions, what was true in 1987 will remain true for the near future.

Behnam Ben Taleblu is a senior fellow at the Foundation for Defense of Democracies.