Seven islands that hold the keys to the Strait of Hormuz

An aerial view of the island of Qeshm, separated from the Iranian mainland by the Clarence Strait, on December 10, 2023. (Nicolas Economou/Reuters via CNN Newsource)

With thousands of U.S. ground troops reportedly on the way to the Middle East, speculation is mounting that they may be assigned to take Iran’s Kharg Island, a key fuel hub in the northern Persian Gulf which handles 90 per cent of Tehran’s oil exports.

But Kharg is just one of dozens of Iranian islands in the gulf, and others may be more important to securing the safe passage of ships – and naval vessels – through the Strait of Hormuz.

Seven of these islands – Abu Musa, Greater Tunb, Lesser Tunb, Hengam, Qeshm, Larak and Hormuz – form what researchers at Sun Yat-sen University in Zhuhai, China, call Iran’s “arch defence.”

“A hypothetical curve connecting these islands would further help to understand Iran’s strategic superiority in controlling the security” of the Hormuz strait, Iranian researcher Enayatollah Yazdani and Chinese researcher Ma Yanzhe wrote in a 2022 paper for the Canadian Center of Science and Education.

Abu Musa, Greater Tunb and Lesser Tunb – the smallest of the seven and at the western end of the arch – are key to strait control, the two researchers wrote.

Because of the limited distance between them and the depth of the water in the largely shallow gulf, “large warships and tankers are forced to walk past” the three islands, the researchers said. That can make them easy targets for Islamic Revolutionary Guard Corps (IRGC) fast-attack boats, mine layers, or drones operating from those islands.

Iranian officials have referred to them and other gulf islands as Tehran’s “stationary and unsinkable aircraft carriers,” Yazdani and Ma wrote.

Last year, the IRGC said it was reinforcing its presence on Abu Musa, Greater Tunb and Lesser Tunb, according to a report from the Foundation for Defense of Democracies.

“Our tactical approach dictates that we must arm and operationalize this group of islands. We have the capability to strike enemy bases, warships, and assets in the region,” IRGC navy commander Rear Adm. Alireza Tangsiri said at the time. (Tangsiri has now been killed in an Israeli operation, Israel and U.S. Central Command said Thursday.)

Because the islands are unsinkable, Iranian military positions on them would have to be eliminated to ensure the safe passage of U.S. warships – potentially those carrying U.S. Marine Expeditionary Units (MEUs) – into the heart of the Persian Gulf, if a landing were to be attempted on Kharg Island.

The islands are “strategically located to control any shipping” trying to leave or enter the gulf, said Hawaii-based analyst Carl Schuster, a former director of the U.S. Pacific Command’s Joint Intelligence Center.

There is no timeline for possible U.S. amphibious assaults on any of Iran’s islands.

U.S. President Donald Trump said Thursday he was extending a deadline for initiating strikes on Iran’s energy infrastructure for 10 days to April 6, to see if a deal could be reached with Tehran to end the fighting. An earlier deadline was set to expire Friday evening, Eastern time.

U.S. Secretary of State Marco Rubio told reporters “progress has been made” in the negotiations with Iran.

But no pause was announced in the overall military campaign. U.S. Defense Secretary Pete Hegseth said Thursday the U.S. would continue “negotiating with bombs.”

CNN has reported that elements of two MEUs – with around 4,000 troops – are on their way to the Middle East. Additionally, some 1,000 troops of the U.S. Army’s 82nd Airborne Division have been alerted to deploy.

Schuster said the full might of these units may be needed to take control of Iran’s key defensive islands. “I would use two MEUs to ensure overwhelming force,” he told CNN.

Getting U.S. troops on the islands would happen in one of two ways – air or sea.

The U.S. Navy ships carry landing craft, including LCACs (Landing Craft Air Cushioned) that can slide up onto beaches to disembark troops and their equipment. But getting them inside the gulf could be a problem as their motherships would have to get past possible Iranian defences on islands earlier in the curve – Hormuz, Larak, Qeshm and Hengam – as well as on the Iranian mainland.

CNN military analyst Cedric Leighton on Thursday said Larak, at the eastern entrance to the strait, presents a problem for naval vessels trying to get into the gulf.

With missiles or small attack craft launched from Larak, “(Iran) could cut off anything that’s going through the strait. This is a critical military target,” he told CNN’s Erin Burnett.

The Navy ships also bring CV-22 Osprey tilt-rotor aircraft that can perform vertical takeoffs and landings along with helicopters. But those aircraft are slow-moving and vulnerable to air defences that earlier airstrikes may have missed.

Troops from the 82nd Airborne could parachute onto the islands from higher-flying aircraft, but such an assault would come with less equipment than can be transported by sea.

All in all, assaults on the islands could take two days to two weeks to complete, but yield important results, if successful, Schuster said.

“Take it, put a radar and some troops on it, you can monitor activity in the strait while denying Iran a staging area for drones and so forth,” Schuster said, of Abu Musa.

A March 24 report from the Institute for the Study of War said U.S. and/or Israeli warplanes had begun attacking Iranian military infrastructure, including aircraft hangars, ports and warehouses on Abu Musa, Greater Tunb and Lesser Tunb – the kind of attacks Schuster said would come before an amphibious invasion.

But taking the islands is just one part of the task. An occupational force of about 1,800 to 2,000 troops would be required to ensure the islands could not be used by the Iranians again, Schuster said.

And that could leave the occupying U.S. troops vulnerable.

“Controlling any of these territories will also require U.S. forces to prevent drone, missile, and artillery attacks from the Iranian mainland, potentially embroiling the U.S. in a longer-term, unpopular engagement on Iranian territory, accompanied by escalating U.S. casualties,” said a new report from the Soufan Center, a New York-based nonpartisan analysis organization.

Schuster called drone and missile defence vital for any U.S. troops on the three Iranian islands.

“If (Iran) has the drones and ballistic missiles available, it will pound any hostile force on those islands,” he said.

But Schuster sees advantages in trying to take the three islands in the lower gulf rather than Kharg, the oil center, in the upper part.

“There is less risk of damaging a future Iranian government’s economy,” he said.

Because most of Iran’s oil flows through Kharg, a fight that damages any of its oil infrastructure could set postwar recovery back years as it’s rebuilt.

Iranian attacks on Qatar’s liquified natural gas facilities earlier this month caused damage that could take up to five years to repair, QatarEnergy officials said.

But analysts said U.S. action to take Abu Musa and Greater and Lesser Tunb could have post-war repercussions, too.

In 1971, Iran, then ruled by the U.S.-supported Shah, took control of the islands as the United Arab Emirates gained independence from colonial Britain.

The UAE has since challenged Tehran’s actions as illegal at the United Nations, and offered to negotiate a settlement of the dispute.

Iran claims it has a historical and geographic right to the islands. The UAE says it may take the dispute to the International Court of Justice, if the matter can’t be resolved.

The U.S. and other nations have been supportive of the UAE in its claim, the UAE Embassy in Washington said in a statement.

And that’s where any U.S. seizure of the islands becomes tricky, Schuster said, calling it a “political dilemma” for Washington with its UAE ally.

If the U.S. returns the island to any new Iranian government, it risks angering the UAE, said Schuster. But he added that if the U.S. returns them to the UAE, it could undermine any perceived legitimacy of the new Iranian regime.

Of course, that’s only a problem if the U.S. succeeds in retaining any seized islands at the end of the conflict. But Schuster said it is something that planners need to consider because it’s the kind of dispute that could see fighting flare anew.

“This is why modern military planning is so complex,” he said.

“Every option has a negative impact. There are no perfect plans or solutions. There is only a balance among costs, risks and impact, both intended and unintended.”

Brad Lendon, CNN