With the US and Israeli military actively degrading the Iranian nuclear weapon programme, it would be a reasonable question to ask whether other Iran might consider use of other non-conventional capabilities, like chemical, biological or radiological (CBR) weapons. If Iran has to make decisions on where to concentrate resources and effort, would someone in the Iranian regime make a ‘nuclear or nothing’ decision, or would they attempt to use chemical, biological or radiological materials in some sort of retaliatory action?

Iran did, historically, have a chemical weapon programme during the latter years of the 1980-88 Iran-Iraq war and admitted to it retrospectively, claiming that it was no longer active. The United States has occasionally claimed that Iran continues chemical weapon research and possibly, biological weapon research, but has done little to publicly substantiate these claims.

The idea that chemical, biological or radiological weapons are somehow a ‘poor man’s nuclear bomb’ has circulated for decades. Some countries have pursued such a strategy in the past. This related to the 1950s idea that, in some way, chemical or biological warfare is some sort of a halfway step between conventional warfare and nuclear warfare. Neither of these beliefs is particularly well founded in the current era. A somewhat deeper dive into CBR warfare is needed to understand why these beliefs are erroneous.

Chemical warfare  

The practical realities of chemical weapon usage in war are fundamentally misunderstood, not just by the general public but by many mainstream military commentators. A practical analysis of extensive data historic instances of chemical warfare combined with modern simulation and modelling yields a few truths:

• Effective chemical weapon use requires the necessary weather conditions and time of day. Particularly in the Gulf, there are many hours in the day, many days in the month and often entire weeks or months in year when chemical weapons do not make any tactical sense to employ.
• Even in the conditions that are ostensibly ideal for employment, subtle and arbitrary changes in local conditions can change the effects of an attack and reduce its effectiveness or hurt the user.
• Since the 1960s, advances in overall lethality of conventional munitions mean that, for any actual practical desired effect, in the majority of tactical situations conventional firepower is of equal or greater effectiveness than chemical weapons.
• With chemical weapons, far more tonnage is needed for use on the battlefield than most people realise. Anything other than a token offensive programme needs to be able to make and stockpile hundreds of tonnes or more of chemical warfare (CW) agent. Single chemical warheads, even large ones on ballistic missiles, are not really very useful weapons for outcomes other than for provocation.
• The industrial footprint and expense required to make those hundreds or thousands of tonnes needs hundreds or thousands of workers, lots of facilities, and will have a very detectable supply chain and a very significant waste disposal problem, all of which would be observable to hostile intelligence.
• Fratricide is an issue regarding the use of chemical weapons and preparations to reduce this, such as troops donning protective clothing, is an immediate and obvious indicator that would trigger the enemy to do the same, thus reducing impact.
• The defensive arms race in CW (masks, suits, detection, decontamination, medical treatment) has spawned far more technical innovation than the historically moribund offensive arms race. Offensive development mostly stopped decades ago. This is a category of warfare in which the perceived adversaries (US, Israel and their allies) have a high degree of defensive capability.

These various factors combine to make chemical weapons a category of munition that is, for battlefield commanders, unreliable, unpredictable, periodically not useful, and in all more fuss for less value than modern conventional weapons. Furthermore, the campaign against Iran is principally an air and naval war so far and not a land conflict. CW against naval targets is largely not a viable concept in any meaningful form. CW against air targets could yield some small value by interdicting airfields, but the amount of persistent agent needed to effectively do so is incompatible with the relatively small payloads of ballistic missiles, while warm Gulf airfields are some of the hottest locations on Earth, reducing the persistency of even the most stubborn chemical agents.

As noted, Iran has historical form in the use of chemical weapons. Iraq also used significant amounts of chemical weapons in its war with Iran, as well as on Kurdish military and civilian targets, who were pawns and victims caught between two larger warring sides. Broader context on the chemical warfare of the era is available here. Iran developed much smaller chemical weapons programme to try to retaliate in kind against Iraq. An exhaustive chronology of historic Iranian chemical issues from the 1980s to 2008 is here. While experts will nit-pick on details, the mainstream consensus is broadly thus:

• The Iranian CW programme in the war was much smaller than the Iraqi programme, both in ambition and in practical scale. It is highly arguable whether or not Iran actually used any chemical weapons in retaliation and some of the allegations that it did are either propaganda or propaganda adjacent.
• The Iranians declared their programme to be terminated when they ratified the chemical weapons convention and joined the Organisation for the Prohibition of Chemical Weapons (OPCW) in the 1990s.
• Experts argue vociferously over the extent to which Iran may or may not have kept a residual CW capability after the 1980-1988 war.
• The Iraqi use of chemical weapons lost much of its tactical utility over time as Iranian defences improved over the course of the war.
• Iran learned a lot from its experience being on the receiving end of CW and developed a lot of practical knowledge on how to mitigate chemical attacks, even with a tight budget and restricted supplies of defensive materiel. This has given the Iranian military a better institutional history and collective memory of the limitations of chemical warfare than most militaries.
• A failed or largely failed chemical attack, such as missile barrages leaving much chemical trace evidence, would be damning and escalatory without any benefit to the regime.

Biological warfare

Biological warfare (BW) has an even more troubled past than CW. Although there are successful instances of CW in the history books, actual use of biological weapons in warfare is almost non-existent. This is an area where popular culture, especially science fiction, has left a large differential between sensationalist claims and the banal reality. Here is the practical reality, based on experience with US and Soviet historic BW programmes and a limited set of BW terrorism incidents:

• As a general rule of thumb, BW agents are less predictable, more susceptible to weather (and the UV rays of sunshine) and far more difficult to reliably disseminate than chemical weapons.
• Very small changes in conditions or dissemination technique can result in a lot of expensive biological material dying or simply being in a form that cannot be absorbed by humans. In theory, the amount of material used in the 2001 anthrax terrorism in the United States was sufficient to kill tens of thousands of people, yet, due to its form and dissemination as well as medical treatment, only five people died. A large dissemination of anthrax by the Japanese cult Aum Shinrikyo resulted in zero fatalities due to technical errors.
• BW agents are more fragile in the environment and susceptible to decontamination, so they have little to no military utility in terrain interdiction, such as trying to use them for area denial (like, for example, persistent chemicals on airfields). Even anthrax spores, the only practical BW candidate for area denial, will die in harsh Gulf sunlight in a few hours.
• Although they are harder to detect than chemical weapons, biological weapons are easier to filter out and rarely require protective suits; just respiratory protection. The collective protection air systems now routinely installed in US naval vessels, for example, are an excellent countermeasure.
• Successful dissemination of BW agents requires a fair bit of open-air trials and such events would be strong indicators of such a programme.

Historical evidence of an Iranian programme in this area, unlike CW, remains scant and speculative. There is no doubt that Iran possesses the life sciences expertise to conduct BW activities, as do many countries. However, given the constraints above, it would be wise to question whether a decision would be made to actually do much. Little solid evidence exists in the public domain beyond accusations. The technical and physical footprint of a research and small-scale production effort is an order of magnitude smaller than a similar CW programme and several orders magnitude smaller than a nuclear programme.

In theory there are several things a BW programme could achieve:

• Anthrax spores can be an annoying and expensive environmental contaminant in buildings, as demonstrated by the 2001 incidents in the United States, but the extent to which that could actually be a major factor in warfare remains speculative.
• Contamination of food and water is a potential vector (Example). Effectively delivering such an attack at scale in a useful way against a distant US enemy is problematic, however.
• On possibility is anti-agricultural warfare. Historically, when the US had an offensive BW programme in the 1940s-1960s, its emphasis gradually shifted to anti-agricultural agents as a method of economic warfare.

With BW, we are left with the CW equation, only worse off for Tehran. The prospect of a failed attack, with a forensic evidence trail leading to the Iranian regime, is probably enough to dissuade Tehran from pushing too far in the BW direction.

Radiological weapons

So-called ‘dirty bombs’, the dissemination of highly radioactive material as a health hazard and environmental contaminant, are largely a damp squib. Nobody can really ever point to this having ever occurred in warfare. Iran, with a commercial nuclear power plant, certainly has access to radioactive materials. The enriched uranium associated with its weapon programme, however, is not actually all that radioactive and not sufficiently hazardous in its own right to be at all useful in this way. Things like radioactive cobalt and caesium are highly radioactive, but, once one does the calculations, the physics do not really support any major military scenarios. Singular acts that contaminate a building or even a city block forcing decontamination, evacuation and possible abandonment are plausible, but only just plausible. Is this possible at scale and in a way that is useful in warfare? Radiological weapons are not really a category of warfare ever seen.

Other considerations

So far this article has discussed acts of warfare, not acts of terrorism. CW, BW and ‘dirty bombs’ have issues of scale that make warfare with unpredictable weapons less palatable and an uncertain return on investment of resources. In the past, Iranian allies have used CW, in particular the former Assad regime in Syria, but would the Iranians trust proxies with CW, BW or radiological material? Certainly, all eyes would be on Iran if various indicators of use were noted. Would the gain be worth any retaliation or escalation?

Another issue is targeting. If the US and/or Israel have any useful intelligence at all on CW or BW infrastructure or capability, they have almost certainly been acting on this intelligence and attacking relevant targets during the broader mayhem.

Finally, there is the issue of deterrence retaliation. The US has periodically, loudly or quietly, often intimated that use of chemical or biological weapons would trigger a nuclear response. Indeed, such hints in diplomatic efforts underpinned some historic chemical and biological arms control diplomacy. Banning CW and BW to remove possible nuclear triggers is a valid diplomatic pursuit.

After all of this discussion, we are back to a ‘nuclear or bust’ discussion. Would any of the CBR weapons short of nuclear weapons be at all useful to Iran? It seems that the most likely approach by Tehran would be to continue the nuclear weapon efforts. A few nuclear weapons could, in fact, force the war to stop or pivot in a way that suited Iran, even without use. CW and BW would not have the same effect.