The Biden administration is reportedly planning to deploy Marines aboard commercial vessels in the Arabian Gulf. This could help deter Iran, demonstrate U.S. commitment to global freedom of navigation and Middle Eastern security, and fuel a push for regional partners to engage more in securing their seas.

However, successfully deploying Marines on commercial ships could require overcoming thorny logistical hurdles, ensuring well-developed command and control, articulating clear rules of engagement, and contingency planning for controlling escalation and de-escalation.

As a maritime nation, America has carried the torch for freedom of navigation around the world. Ensuring the free flow of commerce is vital to the global economy, in particular through Middle Eastern maritime chokepoints in the Gulf. While most oil leaving the Gulf travels to Asian nations, the United States and global markets benefit when this commerce sails smoothly — and suffers when it does not, as evidenced when the Ever Given container ship blocked the Suez Canal and cost an estimated $9.6 billion daily.

Iran and its proxies are among the greatest threats to freedom of navigation in the Middle East, having engaged in more than 40 known cases of malign maritime activity since 2021. Over 20 of these incidents involved commercial vessels, including, since April, the seizure of four oil tankers and the attempted capture of four more. Iran’s maritime aggression routinely includes illegally boarding and seizing ships, swarming vessels with watercraft, and striking ships with drones or other munitions.

Committed to Middle Eastern security, the United States recently sent combat aircraft and over 3,000 Marines to the region, including 100 Marines from the 26th Marine Expeditionary Unit, who can operate on commercial vessels, although President Joe Biden has reportedly not yet approved this initiative.

Placing Marines aboard commercial ships could strengthen deterrence against Iranian seizures and support America’s global freedom-of-navigation aims, as the authors discussed on a Jewish Institute for National Security of America webinar. Marine teams could help defend ships from close passes by other vessels, prevent armed Iranians from boarding the ship, thwart strikes from small Iranian projectiles such as drones, and coordinate naval and air assets against threats.

With Iran likely to probe what ships are carrying Marines and how much force the United States is willing to use, there are potential consequences for deploying Marines on commercial ships, including Iran possibly dragging the United States and regional partners into a broader conflict by retaliating against vessels or military forces.

The success of this plan, therefore, requires careful consideration and decision-making on several issues.

First, U.S. officials could face a decision of where and when to transfer Marines on and off ships in Gulf waters. With Marines typically operating in teams of 15-20, there is a limited number of ships on which they could transit simultaneously. They could deploy on ships at most risk and where they provide the most deterrent effect.

For example, to maximize protection in the critical Strait of Hormuz, Marines could board vessels in the Arabian Sea before they enter the Gulf, disembark inside the Gulf, and reverse the process on ships exiting the Gulf.

Regardless, not publicizing which ships Marines are protecting could increase deterrence: Uncertainty may make Tehran reluctant to seize or attack vessels since it would know if that could lead to conflict with American forces. Programs to place federal air marshals on random commercial aircraft and arm some airline pilots are effective because of similar unpredictability.

Second, in anticipation of Iran probing the United States’ willingness to use force, preparations could include establishing strong command and control between the Marines and U.S. Central Command, as well as setting clear rules of engagement. Publicizing that Marines have the authority to use sufficient force to prevent Iran from seizing, diverting or impairing the free flow of travel could enhance the deployment’s credibility and deterrent effect. Yet, CENTCOM may need contingency plans for escalation and de-escalation if Iranian mischief continues.

Still, U.S. decision-makers should avoid overcommitting assets against aggression not directly affecting Americans or U.S. commerce. America’s Middle Eastern partners need to take on a greater share of the collective responsibility for regional security. The United States should not be more committed to securing oil leaving the Gulf and predominantly headed to Asia than those selling or buying it. Deploying Marines on commercial ships could coincide with a U.S. push to encourage Gulf nations to take a more assertive role in multinational initiatives focused on securing Middle Eastern waters, including the Combined Maritime Forces and International Maritime Security Construct.

Iran has repeatedly shown it will continue disrupting freedom of navigation unless it faces forceful resistance. Small contingents of Marines thoughtfully placed on commercial vessels could change Iran’s nefarious activity, improve regional engagement to support freedom of navigation and promote the free flow of commerce vital to the global economy.

Retired U.S. Navy Vice Adm. Mark I. Fox served as deputy chief of U.S. Central Command. Retired U.S. Marine Corps Lt. Gen. Dave Beydler served as chief of U.S. Marine Forces Central Command. Ari Cicurel is the assistant director of foreign policy at the Jewish Institute for National Security of America.

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