What an influx of 17,000 US troops could mean for the Iran war

If President Trump gives the go-ahead, the U.S. could soon have more than 17,000 ground troops on Iran’s doorstep. That is far short of what would be needed for a full-scale invasion, but they could seize strategic territory on the mainland, secure Tehran’s uranium stockpiles or take an island.

The Pentagon is considering sending another 10,000 ground troops to the Middle East, even as Trump weighs peace talks with Tehran, The Wall Street Journal has reported. That would add to roughly 5,000 Marines and 2,000 paratroopers from the 82nd Airborne Division already ordered to the region. The additional troops would likely include infantry, armored vehicles and logistics support.

That’s far fewer than the 150,000 troops the U.S. deployed in March 2003 to invade Iraq, a country much smaller in terms of both geography and population than Iran.

Trump hasn’t directed the military to put American boots on the ground inside Iran, current and former U.S. officials say. Secretary of State Marco Rubio said Friday he didn’t think they would be needed.

“We are ahead of schedule on most of them, and we can achieve them without any ground troops, without any,” Rubio said in France after meeting with G-7 ministers. But he added that Trump “has to be prepared for multiple contingencies.”

Trump has said he hopes to resolve the conflict through diplomacy and press Iran to agree to a tough set of demands, including handing over its supply of enriched uranium, dismantling key nuclear facilities and reopening the Strait of Hormuz.

But Iran has rebuffed those overtures. Tehran appears to be calculating that closing the strait will pressure the White House to compromise and deter future attacks. The troop buildup could give the U.S. added leverage while preparing for more decisive action if diplomacy stalls, current and former officials said.

“All announcements regarding troop deployments will come from the Department of War,” White House spokeswoman Anna Kelly said. “As we have said, President Trump always has all military options at his disposal.”

If Trump orders the deployment, the troops could be used to seize strategic locations such as the islands off Iran’s southern coast or parts of the coastline. They could also secure the regime’s 970 pounds of enriched uranium that Tehran could use to try to build nuclear weapons.

Each of those missions would be complex and dangerous. A battle for a beachhead near Bandar Abbas, Iran’s main naval headquarters, or for Kharg Island, a crucial oil export hub, would risk significant American casualties, former officials said.

U.S. forces could also target islands around the Strait of Hormuz’s “elbow,” including Abu Musa, Greater Tunb and Lesser Tunb, making it easier to reopen the passageway. From there, they could help shield ships from Iranian missiles and drones and launch land-based strikes against the mainland.

But reaching those areas would be difficult. U.S. ships would have to pass through the strait’s narrow, shallow waters, flanked by Iranian forces armed with missiles and drones and potentially seeded with sea mines. Alternatively, troops could be airlifted from Persian Gulf nations.

The sea approach also offers other dangers. Supersonic antiship missiles could travel from the Iranian mainland in a matter of seconds, while Iran could use its fast attack boats and drones to bombard both naval craft and positions on land, said Seth Jones of the Center for Strategic and International Studies think tank.

“I would be shocked if this could be done without any casualties or commercial or naval ships being hit,” said Jones, a former Defense Department and U.S. Special Operations Command official.

Once on the ground, American forces would need to defend against an array of threats, from Iranian cruise and ballistic missiles and drones launched from boats or from the shoreline. Kharg Island, just 16 miles from the mainland, would require robust air defenses, likely including interceptor-equipped destroyers or sustained air cover.

“That will become a chance to kill Americans who are aggregated and concentrated,” said Mark Montgomery, a retired rear admiral and senior fellow at the Foundation for Defense of Democracies think tank. “They’d be sitting ducks.”

A force of 17,000 troops isn’t enough to hold any location for an extended period, particularly if they are under fire from the regime, said retired Vice Adm. John Miller, a former commander of U.S. naval forces in the Middle East. Those threats would need to be suppressed from the air.

“The longer you are at those locations, you are exposed to greater risk,” Miller said.

By contrast, during the invasion of Iraq in 2003, two Army and Marine U.S. divisions were used to take Baghdad—formations that generally run between 15,000 to 20,000 troops each. On top of that, the U.S. also had a coalition that also contributed ground troops in Iraq. The British sent tens of thousands of troops, which focused on Basra and southern Iraq, including an armored division.

Amid the current conflict, American forces attempting to hold ground in Iran would need to be supported by intelligence, surveillance and reconnaissance assets, as well as logistical support and the capability to evacuate casualties, said retired Gen. Joseph Votel, who formerly commanded U.S. Central Command and U.S. Special Operations Command.

Securing Iran’s stores of enriched uranium could be feasible with special-operations forces and other troops, but it would be a highly complex mission. Much of the material is believed to be buried under the rubble of facilities pummeled in U.S. bombings that Trump ordered last June.

The operation would likely take several days to a week, Votel said. It would require combat troops to secure perimeters, engineers with excavating equipment to search through debris and check for mines and booby traps, and special-operations forces with expertise in handling nuclear material. Unless an airfield was available, a makeshift one would need to be set up to bring equipment in and take the nuclear material out.

“This isn’t a quick in and out kind of deal,” Votel said.

Even if the additional ground troops never move into Iran, the threat to deploy them could serve another purpose: Leverage.

“Job number one is feeding the strategic narrative that we’re serious about this, and the president has options,” Votel said. “There’s clearly a big information component to this.”

Write to Lara Seligman at lara.seligman@wsj.com, Michael R. Gordon at michael.gordon@wsj.com and Alistair MacDonald at Alistair.Macdonald@wsj.com