A suspected piracy incident off the coast of Oman last month quickly turned into an international crisis. On July 29, three armed “suicide drones” attacked the Mercer Street, an Israeli-managed commercial oil tanker.

Two drones missed the tanker during an attempted first strike, but one successfully flew into the Mercer Street’s bridge during a second strike. The attack killed a British security guard and the vessel’s Romanian captain. Here’s what you need to know.

Who did it?

According to the Group of Seven nations and Israel, the “available evidence clearly points to Iran.” This assertion signals the continuation of a U.S.-Iran “shadow war” that has been simmering across the Middle East for the past two years. What is new, however, is the lethality of these attacks and the boldness with which Iranian-made armed drones were deployed against international shipping.

It’s still uncertain who deployed the drones: Perhaps regional proxies launched the attack, or maybe elements of the Iranian armed forces were responsible. Security analysts acknowledge that Iran has become a “drone superpower,” relying on such technologies as the main way it projects power across the region.

From strikes on the government-owned Saudi Aramco oil processing facilities in eastern Saudi Arabia in September 2019 to attacks on U.S. troops in northern Iraq in July 2021, a string of drone strikes ties back to Iran via the technologies used and the known connections of those suspected to be the perpetrators.

With similar evidence after this latest attack, the G-7 and Israel have strongly united against Iran’s “clear violation of international law.” But here’s why Iran’s drone capabilities may be less effective than they might appear.

Iran has used drones to maintain deniability

Since the 1980s, the Iranian drone program has grown to encompass a sophisticated array of military drones produced within Iran. And Iran now supplies armed groups across the Middle East.

This is a deliberate strategy designed to generate “drone deniability” around the deployment of force. By ensuring multiple armed groups in a given region use drones that are the same as or similar to the ones Iran uses, it has become increasingly difficult for the international community to verify who conducted a specific drone strike and, thus, whom to hold accountable.

The attack on the Aramco oil-processing facilities in Saudi Arabia involved Iranian-designed drones and precision missiles. The attack shut off 6 percent of the world’s oil production, sending oil prices up by $11 per barrel. Houthi rebels in Yemen, who had been supplied with Iranian drones and missiles, claimed responsibility for the attack — but other evidence later suggested that Iran was directly responsible. This uncertainty benefited Iran, offering a convenient element of plausible deniability.

There were benefits on the other side, too. As Austin Carson explained here at TMC after the Aramco attack, clouded responsibility helped Saudi Arabia and the West by keeping the conflict from escalating.

Iran and the armed groups it supports continue to engage in attacks

An increasing number of armed groups, with ever-more sophisticated Iranian-designed drones, operate across the Middle East. The use of armed drones by Iraqi militias is a clear example of Iranian-sponsored threats. Attacks have become a monthly occurrence, with reports of strikes on diplomatic sites, international airports and U.S. military bases in April, May, June and July this year. These attacks in fact escalated after a January 2020 U.S. drone strike controversially assassinated Iranian Gen. Qasem Soleimani, whom U.S. officials believed responsible for Iran’s supply of drones.

This drone threat also continues to manifest itself in Yemen, where despite an arms embargo, Houthi rebels have targeted civilians, oil pipelines and military sites in the United Arab Emirates and Saudi Arabia.

Is Iran’s deniability strategy limited?

The attack on the Mercer Street was unusual, however. This took place closer to southern Iranian territory than other lethal attacks.

The United States, Britain, Japan, the European Union, Canada, France, Germany, Israel, Romania and Italy have blamed Iran for the most recent attack. In addition, a U.S. Central Command (CENTCOM) report provides a detailed forensic analysis of drone parts retrieved from the blast site. In this Aug. 6 report, CENTCOM concluded that Shahed-136 drones, produced by Iran and armed with military-grade explosives, were used in the attack on the Mercer Street near the port of Duqm, Oman, and that such an attack was in range of Iranian territory, about 400 miles away.

With so many fingers pointing toward Iran, there appears little room for doubt. Nevertheless, Houthi rebels also have the same drones located around 900 miles away in al-Jawf province, northern Yemen. The Shahed-136’s maximum documented range is around 1,370 miles, making the Mercer Street attack technically within striking distance of this Iranian proxy. Unconfirmed reports and an apparent slip-up by Dana Stroul, U.S. deputy assistant secretary of defense for the Middle East, also implicated Houthi rebels, suggesting that the drones used in the attack were actually launched from Yemen.

Such ambiguity may once again be useful, as Carson argued, offering both the West and Iran a much-needed way out of this tense situation before relations deteriorate to irreparable levels.

Will the “shadow war” burst into the open?

As a result of the strained relationship created by Iranian drone proliferation and the U.S. assassination of a top Iranian official, it has become difficult for each side to effectively communicate, either by the politics of force or diplomacy.

Each side faces a number of challenges in the region but also has a vested interest in keeping matters under control. The U.S. government faces the dilemma of deciding how best to deter Iran without risking escalation — while trying to revive the 2015 Iran nuclear deal. Iran, which still wants the United States and its allies to lift sanctions, has the difficult problem of controlling a beast of its own making: the global spread and miscalculated use of its drone technologies.

Neither difficulty will be resolved easily, but a failure to address these issues risks escalating covert drone actions into overt hostilities.

James Rogers is DIAS assistant professor in war studies within the Center for War Studies at the University of Southern Denmark, and associate fellow within LSE IDEAS at the London School of Economics. Follow him on Twitter @DrJamesRogers.