8 Things To Know About Marine Expeditionary Units

Two U.S. Marine Expeditionary Units (MEUs) are poised to play a role in the Middle East as a tenuous ceasefire takes hold between the United States and Iran. The 31st MEU, based in Okinawa, Japan, arrived in the Middle East on March 28, while the 11th MEU is steaming toward the region after deploying in late March from San Diego, California.

Prior to the April 7 ceasefire announcement, the Trump administration was reportedly considering options for ground operations against Iran, including seizing islands in the Persian Gulf, as part of a larger effort to reopen the Strait of Hormuz.

The arrival of both units will meaningfully expand American military capabilities in the region, but Washington would do well to exercise caution when deciding how best to employ them. Time will tell whether the new combat power will be leveraged at the negotiating table or employed in resumed combat operations against Tehran. Here are eight things to know about MEUs and their Navy counterparts, Amphibious Ready Groups (ARGs).

1. MEUs can perform a range of missions.

The U.S. Marine Corps maintains seven MEUs, each one capable of conducting forcible-entry amphibious assaults — but that is far from their only mission. Each MEU is designed to conduct amphibious landing operations on its own against adversaries on shores around the world, providing the combatant commander a formidable fighting force with robust ground and air capabilities. MEUs are flexible units also capable of conducting limited raids to destroy enemy military infrastructure and defenses; executing precision airstrikes against enemy targets; boarding and seizing vessels; capturing airfields and ports; recovering downed pilots; and supporting naval blockade operations. MEUs can also provide humanitarian and disaster relief or extract Americans from harm’s way in noncombatant evacuation operations (NEOs).

2. MEUs have ground, aviation, logistics, and command elements.

Each MEU’s roughly 2,200 Marines are organized into four parts: a ground force, an aviation element, a logistics element, and a command-and-control unit. Together, they are embarked on an Amphibious Ready Group (ARG) consisting of three ships: an amphibious assault ship (LHD/LHA), an amphibious transport dock (LPD), and a dock landing ship (LSD). The amphibious assault ship is the most capable of the three, resembling a small aircraft carrier that supports both fixed-wing aircraft capable of short or vertical takeoffs, as well as helicopters and tiltrotor aircraft like the MV-22 Osprey. The LPD and LSD play a supporting but critical role, both carrying a well-deck for launching amphibious transport operations and a helicopter pad for rotary-wing and tiltrotor operations.

3. MEU ground forces possess infantry, artillery, and fighting vehicles.

Each MEU ground element is built around a Battalion Landing Team (BLT) of roughly 1,200 Marines, typically including an infantry battalion; an artillery battery with either cannon and rocket artillery (or a combination of both); a mechanized platoon of infantry fighting vehicles called Light Armored Vehicles (LAVs); an assault amphibian platoon with amphibious combat vehicles (ACVs); a combat engineer platoon; and a reconnaissance team.

Modern BLTs can now conduct strikes deep into an enemy’s territory. Artillery batteries can include both HIMARS launchers and M777A2 155mm howitzers. A single HIMARS launcher can fire a pod of six Guided Multiple Launch Rocket System (GMLRS) rockets, two Precision Strike Missiles (PrSM), or one Army Tactical Missile System (ATACMS) missile. This relatively new capability has increased the lethality and range for MEU ground-based fires.

4. MEU air assets include helicopters, tiltrotor, and fixed-wing aircraft.

Each MEU’s aviation element provides assaulting ground troops with close air support and aerial logistics to keep them supplied. It typically includes attack helicopters, logistics lift helicopters, tilt-rotor aircraft, close air support platforms, and fighter aircraft such as impressive F-35B Lightning II jets capable of short takeoff and vertical landing (STOVL). Additionally, the aviation element can perform offensive air support, air reconnaissance, electronic warfare, and forward control of aircraft and ground-based indirect fires. With its organic platforms, MEUs can achieve localized air superiority against most adversaries, and combatant commanders can augment aging AV-8B Harriers and F-35Bs with other aircraft.

5. MEUs provide combatant commanders with increased options.

Because they deploy aboard ships, MEUs can move combat power into a crisis zone relatively quickly without relying on access to foreign air bases or ports. This gives the president and combatant commanders options and flexibility, creating dilemmas for adversaries who cannot easily predict where a MEU might strike. While elements of the 82nd Airborne Division’s Immediate Response Force (IRF) can reach a crisis zone much faster than an MEU, these U.S. Army forces lack the integrated air, naval, and ground firepower that MEUs carry. When both forces deploy together, they can provide even more robust capabilities.  

6. MEUs are built for crisis response, not to conduct sustained combat operations.

An MEU is a rapid-response force, not a combat formation designed to conduct large, sustained operations. With a single infantry battalion and its attached artillery, LAV, ACV, engineer, and reconnaissance elements, an MEU cannot be expected to be successful on its own in sustained large-scale combat operations against a more numerous adversary. MEUs are among the world’s most capable forces at seizing maritime-adjacent territory, but holding that territory against a determined enemy is more difficult, depending on variables including terrain, geography, adversary capabilities, and local civilian considerations. These challenges compound over time without additional support.

7. MEUs require joint combat support for large-scale operations.

The firepower an MEU can bring to bear is less than what is needed for sustained large-scale ground combat operations, lacking heavy armor protection and firepower. In those scenarios, an MEU would need U.S. Army armor and artillery to fill the gap. MEUs once carried tanks, but in 2020 former U.S. Marine Corps Commandant Gen. David Berger removed tanks from the Corps’ inventory in favor of lighter, more mobile capabilities. An MEU’s maneuver elements now consist of light infantry, LAVs, and ACVs, as well as limited artillery and aircraft for fire support. On their own, MEUs must rely on infantry, a limited number of armored ACVs and LAVs, a single battery of towed 155mm artillery or HIMARS launchers, and a relatively small air wing.

8. MEUs require joint logistics support for extended operations.

Each MEU’s logistics element is built to sustain its force with enough fuel, water, food, and ammunition for at least 15 days. For sustained operations, MEUs must rely on other elements of the joint force for resupply. This limits the power-projection capabilities of MEUs and can divert resources from other parts of the joint force. Additionally, the ARGs that MEUs require face their own vulnerabilities. When operating in contested waters, the three-ship formation requires a considerable defensive support network of U.S. Navy destroyers against naval, air, and missile threats. These assets are already stretched thin supporting other global missions, meaning protecting an ARG carries opportunity costs.

Logan Rolleigh is a research assistant at the Center on Military and Political Power (CMPP) at the Foundation for Defense of Democracies (FDD) who served as an active-duty Marine Corps artillery officer. Cameron McMillan is a senior research analyst at CMPP and served as a U.S. Army artillery officer in the Massachusetts Army National Guard. For more analysis from the authors and FDD, please subscribe HERE. Follow FDD on X @FDD. FDD is a Washington, DC-based, nonpartisan research institute focusing on national security and foreign policy.