There’s a crescendo of concern over Syria’s chemical weapons, which the regime has threatened would only be used against “external aggression”.
What’s the historical record on chemical weapons use? Thomas L. McNaugher has a slightly outdated (1990) but still interesting argument in International Security, titled Ballistic Missiles and Chemical Weapons: The Legacy of the Iran-Iraq War:
Beginning in April 1988, in counterattacks against Iranian forces occupying Iraqi territory, Iraq’s forces reportedly used chemical weapons successfully to create panic among Iranian soldiers. Chemical weapons, Robin Wright concluded, were “clearly … a major factor in Baghdad’s stunning victories”. Both technologies [ballistic missiles and chemical weapons] have been credited with bringing Iran to the negotiating table after eight years in which Iranian intransigence, rather than confusion and panic, had been the norm. (p.5)
McNaugher argues, by contrast, that the role of chemical weapons has been overstated: “a strong argument can be made that chemical weapons, even if used, were not essential to Iraq’s successes in these final battles … CW was tricky to use and somewhat unpredictable”, effective mainly against unprotected troops.
Historically, they’ve only worked under narrow conditions:
Chemical weapons were used extensively during World War I, and in lesser quantities by the Italians in Ethiopia in the 1930s and by the Japanese in Manchuria during World War II. They have been used infrequently since, most notably by Egypt in North Yemen in the mid-1960s. They have been tactically useful, but they have produced the kind of panic attributed to Iranian troops in 1988 only against ill-equipped anad untrained soldiers. (p.7)
When Germany first introduced gas in World War I, it caused great panic among British and French forces, but thereafter World War I combatants tended to become inured to the CW threat and also acquired protective equipment. Chemical weapons normally caused panic only among troops that were untrained, ill-equipped, or low in morale for other reasons … chemical weapons acquired their 1988 reputation for dramatic effectiveness [against Iranian forces] from special circumstances that took several years to emerge. (pp.20-21)
Chemical weapons can also be counterproductive if used without care:
Iraq’s initial tactical experiments with chemical weapons in the Iran-Iran war were with nonlethal riot control agents like tear gas. These were introduced into battle in northern Iraq in 1982, with disastrous results; a change in wind direction blew the gas cloud back towards Iraq’s own troops”. (p.17)
As the official British history of World War I put it: gas “made war uncomfortable … to no purpose”.
Update: RUSI’s new Syria report (in which I have a chapter on pathways to regime collapse) includes a contribution from Paul Schulte on chemical weapons. Schulte was formerly Director of Proliferation and Arms Control in the UK Ministry of Defence, and UK Commissioner on the UN Special Commissions for Iraqi Disarmament.
On the likelihood of use and effectiveness:
Use of chemical weapons by the government side, during the fighting seems improbable, except as an act of utter desperation and revenge. Operational solutions to the technical problems of optimal dispersal and necessary persistence in high temperatures would have been practised. The use of any of the CW types available in the government arsenal would probably be devastating against those unprotected insurgents who were in the area under attack. But, as with gunship sorties or heavy artillery bombardment, individual CW attacks against agile and dispersed opponents could not be expected to be strategically decisive, although they would be almost certain to kill significant numbers of intermingled civilians. Such actions would have to be expected to provoke extreme pressures for outside intervention to prevent and punish a crime against humanity. The US has already explicitly strengthened deterrent messages by publicly warning Syria that this would cross ‘a serious red line’.
On a post-Assad regime’s relationship to chemical weapons:
[A] rapid collapse of the Syrian Army and regime and their replacement by a new government, backed by the Free Syrian Army (FSA), with effective control throughout the national territory, would also give little justification for forceful outside involvement. But strong diplomatic efforts could be expected to persuade the new regime, perhaps as a condition of assisting and supplying it, to sign the Chemical Weapons Convention and accept assistance from the Organisation for the Prohibition of Chemical Weapons and friendly states in eliminating its stocks. This would, however, be taken as a regionally controversial pro-Western move. It could not automatically be assumed that a new government (whose composition is unknowable) would willingly opt to eliminate expensive, high salience , national military assets. Elimination is happening in Libya, largely because Qadhafi had already publicly renounced them (though, typically, still retaining undeclared stocks), and the new regime wanted to please NATO nations whose intervention had been critical in overthrowing him ,and wished to signal a generally Western orientation. But a new Syrian government which is looking decreasingly likely to have any similar reason for such gratitude might ’insist on retaining at least some CW stocks as a counter to Israel’s nuclear capabilities and as a bargaining chip in future negotiations over the Golan Heights?’ These are, after all, the kinds continuing geostrategic reason for which they were originally acquired.
Conceivably, also, chemical weapons could be rapidly burnt, exploded, or chemically neutralised, as was done with captured stocks in Iraq by US forces in 1991, and by UNSCOM in the destruction campaign it improvised , under complicated and unsatisfactory political conditions, between June 1992 and June 1994 . Chemical munitions, bulk agent, and precursors stored throughout Iraq were consolidated , and incineration or neutralisation disposed of more than 38,000 filled and unfilled chemical munitions, 690 metric tons of bulk and weaponized CW agents, and over 3,000 metric tons of precursor chemicals. But there would be significant safety hazards to those conducting similar activities within Syria , and resultant accusations of long-term toxic contamination, like those involved in allegations of Gulf War Syndrome after Desert Storm.