Even as US President Donald Trump speaks of “winding down” military action against Iran, there is increasing discussion of using the 31st Marine Expeditionary Unit (MEU), centered on the huge amphibious ship USS Tripoli, to seize and occupy Kharg Island at the northern corner of the Persian Gulf.

The eight square miles of Kharg are largely covered by enormous petroleum storage and piping complexes that move 90 per cent of Iran’s oil exports to sea from the mainland, which is just 15 miles away. While the US has undertaken limited strikes on Kharg, successfully invading it would not only further cripple Iran’s economy, it could also provide a bargaining chip to force Tehran to reopen the Strait of Hormuz at the Gulf’s entrance.

Is this a feasible mission for a Marine force? How risky would it be? And is the bargaining strategy sound?

I grew up in the Marine Corps: My father was a combat infantry officer in the Second World War, Korea and Vietnam. Too bad he’s not around for me to ask these questions, but he deployed to Heaven a few years ago. I know, however, that if I asked him what an MEU can do, his reply would be: “Anything.”

That is a bit hyperbolic, but the three ships of an MEU pack a lot of combat capability. Embarked on the ships are up to 2,500 Marines and Navy sailors, bringing the punch of a full infantry battalion of the highest quality. They also have a strong air-combat element of cutting-edge F-35B Lightning II fighters (the Marine version has short-takeoff and vertical landing capabilities, so no aircraft carrier is required), MV-22B Osprey tiltrotor aircraft (for logistics and air assault), and MH-60S Seahawk helicopters (for scouting, attack and utility missions).

The 31st MEU, based in Okinawa, Japan should arrive late this week; a second Marine force, the 11th MEU centered on USS Boxer, is coming from San Diego and could arrive within three to four weeks. When backed up by the 300 or so combat aircraft already in theater and the more than 20 warships the US is committing to Operation Epic Fury, the MEUs will become powerful new pieces on the chessboard in the Middle East.

The first challenge, before even contemplating boots ashore on Kharg, would be getting the MEU’s ships through the Strait of Hormuz. As they approach the strait, US Central Command (Centcom) will have to assume the ships have been geolocated either by the Iranians or their Russian allies, who are providing very granular intelligence to Tehran. The 31st MEU on the Tripoli will be the top target — both for protecting Kharg and for the publicity and morale boost the Iranians would get for successfully striking the elite force.

My guess is the Tripoli and her naval escorts (two additional amphibious ships, plus two or three guided-missile destroyers) would have to fight their way through the strait. The Iranians would use massive drone attacks; small boats, some loaded with explosives for unmanned and potentially suicide missions; ground-based, short-range ballistic missiles fired from mobile launchers (so-called “scoot and shoot” platforms); and dozens or even hundreds of mines laid in the channel. Centcom would counter with considerable resources, from intelligence collection by long-dwell drones to 24/7 fighter coverage to additional guided-missile escorts to get the ships through the 100-mile transit.

Assuming the expeditionary force traverses the strait without significant loss, the next challenge would be getting to the northern part of the Gulf in the vicinity of Kharg. The Iranians would continue to pepper the ships with drone attacks and might use disguised merchant ships (including the ubiquitous dhow sailboats of the Gulf) for surveillance and potentially for attacks. The Navy’s Fifth Fleet in Bahrain would provide further maritime coverage, and the Gulf Arab states have corvettes and guided-missile patrol boats to help.

Once in position off Kharg, the Marines would need ironclad air and sea superiority over at least 100 miles around the island. Fortunately, Kharg is made of coral (unlike the volcanic sands the Marines faced at Iwo Jima in 1945), meaning it would be hard for the Iranians to dig in and defend. And at the moment it is lightly protected — although this could quickly change.

The recent US strikes have degraded the air and sea defences on the island, which consist of Hawk surface-to-air missiles and Oerlikon anti-aircraft guns. For additional close-air support, the Air Force has deployed A-10 Warthog aircraft and the Army its Apache attack helicopters.

The ground force would probably be landed on Kharg by air, from both Ospreys and helicopters, and it would immediately seek to seize control of the command-and-control facilities, especially those connected with the oil-distribution system. Any Iranian ground troops still effective following pre-attack strikes should be easily overcome by the first waves of US forces. There is fresh water available, a rarity on an island in the Gulf.

Yet there are significant risks and potential pitfalls. There are roughly 20,000 Iranians on the island (almost all civilian oil workers) who would need to be contained in their homes or evacuated; the Iranians may have planted sophisticated booby traps; Iran could successfully strike one of the big amphibious ships (as the Argentines did to the British in the Falklands War in 1982). US casualties would almost certainly rise quickly from the 13 who have so far been killed during Operation Epic Fury.

There is a less risky option probably under consideration: To use the MEU to blockade the island rather than seize it, which would likely result in fewer casualties and could achieve a similar economic effect.

Finally, if the idea is to then bargain with Tehran for an opening of the Strait of Hormuz, it is unclear that the remaining leaders of the regime would be cowed by the threat of losing Kharg. They know the US, which they consider totally untrustworthy, could blow up the island any time, regardless of any agreement. So, they might balk at agreeing to give up anything for Kharg and continue pressuring the US through a tighter closure of the strait.

Can the Marines take Kharg, and add its conquest to their impressive history of seizing and holding distant islands? I wouldn’t bet against them.

But such an invasion would likely be far from surgical — expect rising casualties on both sides and among civilians — and still leave Iran with plenty of other potential steps to create mayhem and improve its bargaining position.

· Admiral James Stavridis is a former Supreme Allied Commander, Europe and dean emeritus of the Fletcher School of Law and Diplomacy at Tufts University.