… it is far easier to protect against chemical munitions than against an equivalent amount of high explosives, a point made by Matthew Meselson. Let’s unpack that, because I think folks generally have an unrealistic assessment of the power of a chemical weapon attack, imagining tiny amounts to be capable of producing mass casualties. Now chemical munition agents have a wide range of lethalities and concentrations, but let’s use Sarin – one of the more lethal common agents, as an example. Sarin gas is an extremely lethal agent, evaporating rapidly into the air from a liquid form. It has an LD50 (the dose at which half of humans in contact will be killed) of less than 40mg per cubic meter (over 2 minutes of exposure) for a human. Dangerous stuff – as a nerve agent, one of the more lethal chemical munitions; for comparison it is something like 30 times more lethal than mustard gas.

But let’s put that in a real-world context. Five Japanese doomsday cultists used about five liters of sarin in a terror attack on a Tokyo Subway in 1995, deployed, in this case, in a contained area, packed full to the brim with people – a potential worst-case (from our point of view; “best” case from the attackers point of view) situation. But the attack killed only 12 people and injured about a thousand. Those are tragic, horrible numbers to be sure – but statistically insignificant in a battlefield situation. And no army could count on ever being given the kind of high-vulnerability environment like a subway station in an actual war.

In order to produce mass casualties in battlefield conditions, a chemical attacker has to deploy tons – and I mean that word literally – of this stuff. Chemical weapons barrages in the First World War involved thousands and tens of thousands of shells – and still didn’t produce a high fatality rate (though the deaths that did occur were terrible). But once you are talking about producing tens of thousands of tons of this stuff and distributing it to front-line combat units in the event of a war, you have introduced all sorts of other problems. One of the biggest is shelf-life: most nerve gasses (which tend to have very high lethality) are not only very expensive to produce in quantity, they have very short shelf-lives. The other option is mustard gas – cheaper, with a long shelf-life, but required in vast quantities (during WWII, when just about every power stockpiled the stuff, the stockpiles were typically in the many tens of thousands of tons range, to give a sense of how much it was thought would be required – and then think about delivering those munitions).

[…]

But that’s not the only problem – the other problem is doctrine. Remember that the modern system is all about fast movement. I don’t want to get too deep into maneuver-warfare doctrine (one of these days!) but in most of its modern forms (e.g. AirLand Battle, Deep Battle, etc) it aims to avoid the stalemate of static warfare by accelerating the tempo of the battle beyond the defender’s ability to cope with, eventually (it is hoped) leading the front to decompose as command and control breaks down.

And chemical weapons are just not great for this. Active use of chemical weapons – even by your own side – poses all sorts of issues to an army that is trying to move fast and break things. This problem actually emerged back in WWI: even if your chemical attack breaks the enemy front lines, the residue of the attack is now an obstruction for you. […] A modern system army, even if it is on the defensive operationally, is going to want to make a lot of tactical offensives (counterattacks, spoiling attacks). Turning the battle into a slow-moving mush of long-lasting chemical munitions (like mustard gas!) is counterproductive.

But that leaves the fast-dispersing nerve agents, like sarin. Which are very expensive, hard to store, hard to provision in quantity and – oh yes – still less effective than high explosives when facing another expensive, modern system army, which is likely to be very well protected against such munitions (for instance, most modern armored vehicles are designed to be functionally immune to chemical munitions assuming they are buttoned up).

This impression is borne out by the history of chemical weapons; for top-tier armies, just over a century of being a solution in search of a problem. The stalemate of WWI produced a frantic search for solutions – far from being stupidly complacent (as is often the pop-history version of WWI), many commanders were desperately searching for something, anything to break the bloody stalemate and restore mobility. We tend to remember the successful innovations – armor, infiltration tactics, airpower – because they shape subsequent warfare. But at the time, there were a host of efforts: highly planned bite-and-hold assaults, drawn out brutal et continu efforts, dirigibles, mining and sapping, ultra-massive artillery barrages (trying a wide variety of shell-types and weights). And, of course, gas. Gas sits in the second category: one more innovation which failed to break the trench stalemate. In the end, even in WWI, it wasn’t any more effective than an equivalent amount of high explosives (as the relative casualty figures attest). Tanks and infiltration tactics – that is to say, the modern system – succeeded where gas failed, in breaking the trench stalemate, with its superiority at the role demonstrated vividly in WWII.

Bret Devereaux, “Collections: Why Don’t We Use Chemical Weapons Anymore?”, A Collection of Unmitigated Pedantry, 2020-03-20.