There is no mystery as to why folk thought Saddam might have chemical WMDs in the early 1990's: (a) he definitely once had a complement of Scuds (and used them against Israel in 1991); and (b) he definitely had a CW capability, which he had used extensively against the Iranians in the 1980's, not to mention his 'own people'.
But - and it's a big, big But - this was a tactical CW capability, not 'MD' at all.
It was in fact quite an advanced tactical capability, consistent with several competent aspects of the 1980's Iraqi military as I'll explain. But, to round off the present-day aspect: it's no surprise to find ISIL using CW, because their mainstream fighting capability is based on a core (indeed, a corps) of fairly proficient Iraqi army officers of the Saddam era, whose combat experience is second to none on the planet. Likewise, I am guessing there will be no shortage of Iranian soldiers who will recall Saddam's gas attacks from bitter personal experience - and may know what to do about them as well.
* * * *
Back in 1982, Saddam had a problem. He'd attacked Iran in 1980 on the assumption it would be weakened by the anti-Shah revolution: but it turned out to be a hornet's nest, and soon he was facing an invasion from the other side, human-wave assaults from berserker revolutionary guards and all.
Saddam's boys came up with a truly novel device. When they were about to use chemicals, their own front-line troops foregathered in tents containing a massive slab of ice. They would suit up and sit around the slab remaining cool - literally - until the order came to storm into the gassed Iranian position; do the business ASAP; then fall back and strip off.
(Ingeniously, the blocks of ice served another purpose. As with the British Army on which they were modelled, Iraqi infantry units were raised geographically. Thus, as in WW1, there was always the possibility of mass casualties being suffered amongst a cohort all hailing from the same town or district, with the distinct possibility of unrest at home if a large number of bodies were sent back all at once. So the ice was used to get the bodies back to a depot in decent order, whence they were released to their relatives in dribs and drabs over several ensuing months.)
The ice trick is not the only example of striking innovation in Saddam's military. I'll mention two more.
- the Iraqi high command formed the view that the generals who were the best at, say, conducting an offensive, were not necessarily as well suited to organising a defence. The logical development of this plausible observation was to coin the notion of commanders with recognised specialisations. They would be deployed accordingly, and substituted when the battle moved onto a different phase. I know of no other army that has used this doctrine (does anyone else?)
- they were being forced to fight along a much wider front than was comfortable, and tanks were a precious commodity. It was determind that they were to be used only at the optimal point in the battle, then swiftly withdrawn for redeployment elsewhere. To achieve this on a strategic scale, Iraq invested in the greatest fleet of low-loaders known to man. This is not an entirely novel doctrine: Israel reckons to be able to switch forces between its eastern and western fronts very rapidly, too. But the distances involved are much less.
*why are they called 'improvised' EDs ? They may have been once, back in Afghanistan in 2002, but not any more.