Do Aircraft Carriers Deter Iran?

For many years now, sending aircraft carriers to the Persian Gulf region has been the go-to option during periods of tension with Iran, whether to deter the regime, shape its conduct, or deal with the aftermath if deterrence fails. Yet there is no evidence that such measures have effectively deterred Tehran and its proxies—instead, the practice of frequent, extended, back-to-back deployments has overworked ships and their crews, played havoc with deployment and maintenance schedules, and prevented the U.S. Navy from meeting its growing commitments in the Indo-Pacific region. As the United States works to right-size its military presence in the Middle East, these issues have become a key concern for policymakers intent on countering a rising China and a resurgent Russia.

Since the 1991 Gulf War, the Navy has generally kept at least one of its ten operational aircraft carriers in the region (organized into a carrier strike group with 36-48 strike aircraft, a cruiser, and 3-4 destroyers), along with one of its ten or so amphibious assault ships (a small aircraft carrier organized into an amphibious ready group with 6 strike aircraft, an amphibious transport dock, and a dock landing ship). But never once during this period have carrier aircraft launched strikes in response to Iranian-linked attacks on U.S. interests, of which there have been many—the 1996 Khobar Towers bombing in Saudi Arabia, attributed to Lebanese Hezbollah and Iran; numerous attacks by pro-Iran militias that killed more than 600 Americans in Iraq after 2003; and scores of rocket attacks on the U.S. embassy and American military personnel in Iraq since 2019, resulting in the deaths of at least four Americans. Indeed, some of Iran’s most audacious activities in recent years have occurred when the United States had one or two carriers in the Gulf region:

• June 2019: Iran conducts a limpet mine attack on two petrochemical tankers in the Gulf of Oman and shoots down a Global Hawk drone in the Persian Gulf.
• September 2019: Iran conducts a drone and cruise missile strike on Saudi oil facilities at Abqaiq and Khurais.
• December 2019: Pro-Iran militias ramp up rocket attacks on U.S. forces in Iraq, killing an American civilian contractor.
• January 2020: Iran retaliates for the killing of Qods Force commander Qasem Soleimani in a U.S. drone strike by launching sixteen missiles at al-Asad Air Base in Iraq, inflicting traumatic brain injuries on more than a hundred U.S. airmen.
• March 2020: Pro-Iran militias kill three coalition soldiers (two Americans, one Briton) in a rocket attack on Camp Taji in Iraq.
• June 2020: Tehran reportedly initiates a plot to kidnap Iranian American activist Masih Alinejad on U.S. soil and bring her to the Islamic Republic.

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There have been times, however, when the assertive use of carriers has deterred Iranian actions. In April 2015, an Iranian naval convoy attempting to deliver arms to Houthi forces in Yemen turned back after a carrier strike group and amphibious ready group converged on it. The U.S. vessels sent aircraft on routine daily flybys near the convoy to generate persistent pressure. Iran subsequently sent a “humanitarian” convoy in a show of defiance while it pursued less risky means of delivering arms to the Houthis.

The United States has apparently found other ways to deter Iran as well. After it established a multinational maritime security force in September 2019 to ensure freedom of navigation in the Persian Gulf (followed by a parallel European effort in February 2020), attacks on shipping decreased dramatically. U.S. Central Command chief Gen. Kenneth McKenzie Jr. attributed the decrease to the presence of surveillance assets associated with the maritime security forces, which greatly reduced the possibility of deniable attacks by Iran—the ultimate form of deterrence by denial.

More than anything, what seems to have deterred certain destabilizing Iranian activities since early 2020 was the credibility created by the killing of Soleimani. Following his death, Tehran acted with increased caution—though after several months it again began carefully probing U.S. response thresholds. In September 2020, and again in December, the United States threatened to shutter its Baghdad embassy if proxy rocket attacks continued; the potential withdrawal of the remaining civilian personnel there was apparently perceived as a sign of Washington’s willingness to escalate militarily. In response, Iran’s proxies dramatically scaled down rocket strikes on the embassy and U.S. troops, substituting improvised explosive device attacks on coalition logistical convoys manned by Iraqi contractors.

Thus, the shock of Soleimani’s death, the embassy closure threat, and concerns that President Trump might lash out before or after the November election seem to have altered Tehran’s risk calculus. These developments also set Iran and its proxies on their heels, eliminated two perhaps irreplaceable operators (Soleimani and militia leader Abu Mahdi al-Muhandis, who was killed in the same 2020 strike), and emboldened those Iraqis who oppose Iranian influence over their country—underscoring that deterrence is but one factor to consider when evaluating the efficacy of U.S. policy; disrupting an adversary’s operations, strategy, and policy may sometimes be just as important.

Moreover, experience shows that it is not so much the size or capability of forward-deployed forces that deters, but rather the credibility of U.S. deterrent threats. Washington can surge forces into the region when necessary, but it cannot surge credibility, which must be cultivated by consistent shows of resolve. As U.S. attention and forces increasingly focus on the Indo-Pacific, policymakers need to ascertain whether a lighter but more actively employed Gulf force may deter Iran more effectively than carriers conducting presence patrols. At the same time, the United States is a great power with global commitments; it cannot respond to every challenge by regional adversaries, nor should it try to.

Ultimately, success in these situations is measured not by whether U.S. actions deter all adversary activities, but whether they deter its most destabilizing activities, forcing the adversary to employ less disruptive means. During its final months in office, the Trump administration accomplished this when pro-Iran militias ramped down rocket attacks on U.S. sites and ramped up largely nonlethal attacks on Iraqi-manned convoys—a kind of “performative resistance” that enabled them to strike a defiant pose without incurring significant risk of U.S. escalation. After President Biden’s inauguration, however, these proxies embarked on an epidemic of rocket and drone attacks that threatened U.S. personnel, to see what they could get away with.

Such tests will likely proliferate in the future. Washington’s decision to withdraw from Afghanistan and draw down U.S. missile defenses and fighter aircraft in Jordan and the Gulf could encourage Tehran to intensify pressure on the United States and try to further expand its regional influence—especially now that hardline president Ebrahim Raisi has entered office. To better deter, shape, and respond to such challenges, U.S. policymakers should emphasize the following elements:

Assurance and contingency response. Carriers may not generally deter Tehran, but their presence might alter its risk calculus and provide other benefits. Deploying light carrier groups to fill the likely gap between future supercarrier deployments to the region can help shape Iran’s conduct, assure regional partners (while steering them away from destabilizing actions of their own), and provide a forward-deployed contingency response capability. These light carrier groups would consist of amphibious assault ships with up to 20 F-35B Lightning stealth fighters (the Navy’s so-called “Lightning Carrier” concept) accompanied by destroyer escorts. The F-35Bs would afford gray zone options not offered by the mainly nonstealthy aircraft aboard supercarriers.

A smaller, more active presence. A smaller joint force consisting of Army, Navy, and Air Force assets employed more actively, and bolstered by nonmilitary deterrence measures, might more effectively deter and shape Iranian behavior. In the event of escalation with Iran, reinforcements could always be surged into the region. Responding more consistently to challenges would demonstrate U.S. commitment and resolve, while acting more unpredictably would complicate Iran’s efforts to manage risk and might cause it to act with more caution. In pursuing this approach, the United States should target assets that Tehran truly values (imposing material costs—and taking lives only in response to U.S. loss of life) in order to exact an unfavorable cost-benefit ratio on Iran’s actions. Relying on both deterrence by punishment and deterrence by denial will likely yield better outcomes than relying on just one or the other.

Mastering the gray zone. By operating primarily in the gray zone—via covert or unacknowledged activities, both nonkinetic and kinetic—Washington can confront Iranian officials with many of the same attribution and accountability dilemmas they have long posed for U.S. policymakers. Because such activities can be carried out by a relatively small force, a U.S. gray zone deterrence strategy would likely be more effective and sustainable than approaches that rely on deploying carriers and heavy bombers to the Gulf. And since many of these activities occur below the radar screen, they are less likely to hinder diplomacy with Iran, roil U.S. domestic politics, unsettle regional partners, or result in a broader conflict—even as they free up supercarriers to counter China and Russia.

Michael Eisenstadt is the Kahn Fellow and director of the Military and Security Studies Program at The Washington Institute. Henry Mihm is a former research assistant with the program. Parts of this PolicyWatch are drawn from the recent Institute publication “Deterring Iran in the Gray Zone: Insights from Four Decades of Conflict.”