Iran’s Chemical and Biological Options in a U.S. Ground Invasion

The Hidden Catastrophe: Iran’s Chemical and Biological Options in a U.S. Ground Invasion

The intensifying military campaign against Iran has focused global attention on nuclear escalation, regional instability, and the humanitarian consequences of a widening conflict. Yet beneath these visible dangers lies a quieter, more insidious threat—one that could transform a conventional intervention into a strategic calamity. If the United States were to commit ground forces to Iranian territory or attempt to seize key islands in the Persian Gulf, Washington must confront the possibility that Iran could employ chemical or biological agents against concentrated formations of Marines and soldiers. The consequences would be devastating not only for the forces involved but also for the political relationship between the American government and its citizens. A mass‑casualty event triggered by chemical or biological weapons would challenge national resolve, disrupt operational timelines, and potentially leave the United States in a worse strategic position than before the conflict began.^[i]

Iran could at least develop chemical weapons any time, if they haven’t already

Iran’s history with chemical weapons is neither speculative nor abstract. During the Iran–Iraq War, the Islamic Republic was the victim of repeated Iraqi chemical attacks, and although Tehran publicly renounced chemical weapons after the war, open‑source assessments and intelligence analyses have long suggested that Iran retained at least a latent capability. Reports from think tanks, defense analysts, and journalists have pointed to research into pharmaceutical‑based agents, riot‑control chemicals, and dual‑use precursors that could be weaponized under wartime conditions.^[ii] Iran’s investment in asymmetric warfare—ballistic missiles, drones, proxy militias, and cyber operations—makes it reasonable to assume that chemical and biological options would be viewed as tools of last resort in the face of a U.S. invasion.^[iii]

Strategy

The strategic logic is straightforward. Iran cannot defeat the United States in a conventional ground fight. But it can impose unacceptable costs. Chemical or biological attacks on U.S. forces would not be designed to achieve battlefield victory; they would be intended to break political will. The United States has not suffered mass casualties from weapons of mass destruction since World War I. A single successful attack on a battalion‑sized element of Marines or paratroopers—especially in a confined battlespace like an island seizure—could kill or incapacitate hundreds. The psychological shock alone would reverberate across the American public, raising questions about the wisdom of the intervention, the adequacy of preparation, and the competence of national leadership.^[iv]

This risk becomes even more acute when considering the likely employment of U.S. forces in the opening phase of a conflict. Any serious plan to degrade Iran’s military capabilities or secure the Strait of Hormuz would require the rapid seizure of key islands: Abu Musa, Greater Tunb, Lesser Tunb, and potentially Kharg Island. These islands are small, heavily surveilled, and within range of Iranian missile, drone, and unconventional weapons delivery systems. Their capture would almost certainly fall to the Marine Corps and the 82nd Airborne Division—the two U.S. forces most capable of executing rapid forcible entry operations under fire.^[v]

Rules of engagement for Marines and Airborne forces

For the Marine Corps, this mission aligns with the logic of Expeditionary Advanced Base Operations (EABO) and the broader framework of Force Design 2030. FD2030 envisions small, distributed units capable of seizing and holding key maritime terrain, operating inside contested zones, and enabling naval campaigns.^[vi] Yet the very attributes that make these units agile—light equipment, limited organic sustainment, and reliance on external logistics—also make them vulnerable in a chemical or biological environment. Marines operating on Abu Musa or the Tunbs would be isolated, dependent on naval resupply, and exposed to Iranian fires. If Iran employed chemical agents delivered by artillery, rockets, or drones, the Marines’ ability to maintain tempo, communicate effectively, and sustain themselves would degrade rapidly.^[vii]

The 82nd Airborne faces similar challenges. Although unmatched in its ability to deploy quickly and seize airheads, the division is not optimized for prolonged operations in a contaminated environment. Airborne forces rely on speed, surprise, and rapid buildup of combat power. Chemical contamination undermines all three. Paratroopers landing on a chemically saturated drop zone would face immediate casualties, disorientation, and equipment degradation. Even if the initial assault succeeded, sustaining an airborne lodgment under chemical threat would require massive logistical support—decontamination assets, protective gear resupply, medical evacuation, and specialized engineering units.^[viii]

Small islands

The geography of the islands compounds these vulnerabilities. Abu Musa is only about ten square miles; Greater Tunb and Lesser Tunb are even smaller. These confined spaces offer no depth, no maneuver room, and no ability to disperse forces. A single chemical strike could blanket the entire island. The Marines and paratroopers would be forced into a defensive posture, donning protective gear that reduces mobility, slows reaction times, and increases fatigue. Communications equipment—already strained by Iranian jamming and electromagnetic warfare—would suffer from contamination and environmental degradation.^[ix]

Logistics

Logistics, the lifeblood of any military operation, becomes a nightmare under these conditions. Resupply convoys or aircraft must undergo decontamination, slowing the flow of materiel. Water, food, and medical supplies must be protected from contamination. Casualty evacuation becomes perilous, as helicopters risk spreading agents or becoming contaminated themselves. The Navy’s ability to support these operations from offshore platforms would be constrained by the need to avoid contamination of ships—assets that cannot easily be decontaminated at sea.^[x]

At this point, the operational risks intersect with a deeper strategic warning—one that predates modern doctrine. The debate now consuming defense analysts and retired generals centers on whether the United States should seize Kharg Island, force open the Strait of Hormuz or attempt both simultaneously. The tactical case is seductive: Kharg Island handles the overwhelming majority of Iran’s crude exports, and the Strait is the economic jugular of the entire Gulf. With Marines and the 82nd Airborne moving into position after a month of successful air operations, the temptation to deliver a decisive, visible blow is powerful. But temptation is not strategy. The oldest military treatise in the world warns against mistaking momentum for wisdom.^[xi]

War is Art, Not Rhetoric

The principles articulated in The Art of War endure precisely because they illuminate moments like this. Iran has spent nearly half a century preparing the Gulf for the kind of operation now being debated on cable news panels. Every island, every chokepoint, every approach lane into the Strait has been shaped, mined, tunneled, and fortified with the expectation that one day the United States might try to force its way in. To assault Kharg Island or attempt to pry open the Strait is to walk directly into a battlespace the enemy has spent decades designing. No strategist—ancient or modern—would recommend attacking a fortified position on constricted ground, under the enemy’s surveillance, on the enemy’s timeline, and with only one exit behind you. Yet that is precisely what an amphibious or airborne assault inside the Persian Gulf would entail.^[xii]

The ancient warning is simple: do not attack where the enemy is strongest, do not fight on ground from which retreat is impossible, and do not allow the adversary to dictate the terms of battle. Iran’s strategy is to lure the United States into a narrow, predictable, geographically constrained fight where its missiles, mines, drones, and unconventional weapons can inflict maximum political and psychological damage. If Washington chooses that fight, it will be choosing the enemy’s strategy over its own.

Hitting Iran where it is vulnerable

The United States has options—real ones, powerful ones—that strike at Iranian vulnerabilities rather than Iranian strengths. Those options exist outside the narrow frame of Kharg Island and the Strait of Hormuz. They are the kinds of pressure points that Sun Tzu would recognize instantly: indirect, asymmetric, and strategically disorienting to the adversary. They are also the kinds of options that should never be discussed publicly. But their existence is a reminder that the most decisive victories are often the ones achieved without storming the gates the enemy has spent a lifetime reinforcing.^[xiii]

Iran understands these vulnerabilities. Its military doctrine emphasizes asymmetric responses to superior conventional forces, and its leadership has repeatedly signaled that it views U.S. ground forces as the most politically sensitive target. The use of chemical or biological agents would be framed as a defensive necessity, a desperate measure to repel invaders. Tehran would likely deny responsibility, blame proxies, or claim accidental release. The ambiguity surrounding attribution—especially with biological agents—would complicate U.S. decision‑making and delay retaliation.^[xiv]

Political Consequences

The political consequences at home could be severe. The American public has grown accustomed to limited‑casualty conflicts. A sudden mass‑casualty event involving chemical or biological weapons would shock the national conscience. Families would demand answers. Congress would launch investigations. Media coverage would amplify every failure in planning, preparation, and execution. The administration—regardless of party—would face intense pressure to withdraw, escalate, or both. The unity of purpose required for a sustained campaign could fracture.^[xv]

This is not an argument against military action. It is an argument for realism. If the United States is to consider ground operations against Iran, it must plan for the worst‑case scenario. That means equipping Marines and soldiers with the protective gear, detection systems, and decontamination assets necessary to operate in a contaminated environment. It means rehearsing island‑seizure operations under chemical threat conditions. It means ensuring that MEU/ARG formations and airborne brigades have the logistical depth to sustain themselves even when resupply is slowed or disrupted. It means integrating CBRN considerations into every level of planning—from strategic objectives to tactical execution.^[xvi]

Proceed with Caution

Above all, it means acknowledging that Iran’s chemical and biological capabilities, while often overshadowed by its nuclear ambitions, represent a real and present danger. The United States cannot afford to be surprised. The cost of underestimating this threat would be measured not only in lives lost but in strategic failure. A military campaign that begins with confidence could end in chaos if chemical or biological weapons are unleashed on unprepared forces. The American people deserve better. The Marines and soldiers who may one day be ordered to seize Abu Musa, the Tunbs, or Kharg Island deserve better. And the nation’s leaders must ensure that any plan for ground operations in Iran accounts for the full spectrum of threats—not just the ones that are easiest to see.

Notes:

[i] Steve Balestrieri. “Does Iran Have Chemical Weapons?” National Security Journal. June 23, 2025.

[ii] Andrea Stricker. “Countering Iran’s Covert Chemical Weapons Program.” Foundation for Defense of Democracies. Research Memo. February 24, 2026.

[iii] Ilma Athar Ali. “More Deadly Than Missiles: Does Iran Have Chemical or Other Unconventional Weapons?” WION News. January 14, 2026.

[iv] Kenneth Katzman. Iran’s Foreign and Defense Policies. Congressional Research Service. January 11, 2021.

[v] JP 3‑18, Joint Forcible Entry Operations.

[vi] U.S. Marine Corps, Force Design 2030.

[vii] RUSI, “The Threat No One Is Talking About: Iran.”

[viii] JP 3‑11, Operations in Chemical, Biological, Radiological, and Nuclear Environments.

[ix] Hamish de Bretton-Gordon. “Iran has not yet used its nastiest weapon. We should be ready when it does.” The Telegraph. 24 March 2026.

[x] GAO, Chemical and Biological Defense: DOD Needs to Strengthen Preparedness.

[xi] Sun Tzu, The Art of War.

[xii] Michael Peck. “Iran Has Likely Developed Fentanyl-based Chemical Weapons.” Business Insider. November 2024.

[xiii] Sun Tzu, The Art of War, op. cit.

[xiv] DIA, Iran Military Power.

[xv] CRS, U.S. Military Operations and Congressional Oversight.

[xvi] JP 5‑0, Joint Planning.

This article was originally published by RealClearDefense and made available via RealClearWire.