Other units include around 100 Marines from the Second Battalion, Seventh Marine Regiment. The company-size contingent is deployed to Kuwait as part of a special purpose task force meant to respond to emergencies in the Middle East. The Marines, fresh off helping American forces withdraw from northeastern Syria, are reinforcing dozens of security personnel positioned at the American Embassy in Baghdad. The compound is large, more than 100 acres, with guard posts, living areas, dining halls and small shops.

Around 100 Army Rangers from the 75th Ranger Regiment deployed shortly after last week’s drone strike. The Rangers, part of the secretive Joint Special Operations Command, most likely will act as a reaction force if any Iranian-backed forces launch a concerted attack on an American position, according to one Defense Department official.

The 26th Marine Expeditionary Unit includes roughly 2,200 Marines and sailors, composed of an infantry battalion, logistics unit and a squadron of aircraft, namely transport helicopters and attack jets. They are aboard Navy ships in the Bataan Amphibious Ready Group, made up of around 2,000 sailors, and are steaming toward the Middle East as part of a previously scheduled deployment.

These Marine Expeditionary Units have long served as a global response force. Often their deployments in the Persian Gulf have found them supporting operations in Iraq, Syria and Afghanistan.

The Troops Already in the Region

There are between 45,000 and 65,000 American military personnel — the number can vary by the day — now deployed in Saudi Arabia and other Persian Gulf nations, including around 5,500 troops in Iraq and 600 in Syria.

In response to Iranian attacks and provocations since May, the Pentagon deployed about 14,000 additional troops to the Persian Gulf region, including roughly 3,500 more to Saudi Arabia. The military assets include early warning aircraft, maritime patrol planes, Patriot air and missile defense batteries, B-52 bombers, a carrier strike group, armed Reaper drones and other engineering and support personnel.

Roughly 2,000 American troops are in Turkey, mostly based at Incirlik Air Base. Despite recent tensions with the fellow NATO country, the United States has continued to use the airfield. American aircraft launched hundreds of combat sorties from the base at the height of the conflict against the Islamic State in 2016 and 2017.