Bombs away: The sarin shell/IED is, I think, being misplayed by both sides. One side insists that the discovery of the sarin shell is conclusive evidence of deployable WMD in Saddam's Iraq; the other side sees it as a story that can be safely ignored, saying that a single artillery shell isn't evidence of a real stockpile. To understand why I think neither position is correct, we have to follow the development of sarin weapons in Saddam's Iraq.

Sarin (GB) isn't easy to keep around; not only do impurities in the chemical eventually cause it to break down into a less-toxic form, but the hydrofluoric acid in it eats through any metal containers it's placed in. Prior to Gulf I, the CIA issued an NFE intel brief noting that, due to the short shelf life of Iraq's sarin stocks, Saddam had embarked on a crash program to both improve the quality of its sarin and to create a binary sarin weapon.

A binary chemical weapon is one that mixes two chemicals -- generally more stable and less harmful than the final result -- to create the chemical toxin. In the case of Iraq's GB/GF weapons, methylphosphonic difluoride, or DF, is mixed with an isopropyl alcohol/isopropylamine solution, or OPA to create a sarin mixture. The advantage is obvious: binary weapons keep longer and are easier to handle -- as long as you can engineer a decent warhead to deliver them in.

Sarin was the primary deadly chemical weapon of Iraq's arsenal. In 1985, when it had switched almost entirely to sarin as its nerve gas of choice, an Iraqi military document obtained by the CIA said that "12,571 155mm sarin bombs can be loaded in ... five months (using 44,000 liters of sarin to be produced during these months)." Of course, by 1985, the "war of the cities" was underway, Iran was capturing critical lands from Iraq, and there was no reason to keep chemical weapons sitting in arsenals. By the late 1980s, with Saddam looking towards the future, the need for long-term storage of Iraq's weapons of mass destruction was more obvious.

Iraq had two designs for binary delivery of chemical weapons: a crude method and a sophisticated method. The sophisticated method was not unlike the chemical artillery shells developed by the United States in the 1960s and '70s, and by the Soviet Union and its successor states perhaps as late as the 1990s. In this design, two compartments hold the DF and OPA, and the rotation of the shell in flight mixes them.

As with Iraq's other major chemical weapon, mustard gas, these were 155mm artillery shells, the same kind found in the roadside IED. These shells were engineered and tested from 1983 to 1990 -- the inspectors found several shells at the Muthanna State Establishment in 1996 -- but, according to Iraq's declaration and internal documents obtained by UNSCOM, never quite successful enough to warrant large-scale production.

Instead, Iraq concentrated on an effective but crude design. Designed into both rocket warheads and R-400 9-liter bombs, this design kept the weapons primed with the OPA alcohol solution. Just before launching, the DF component would be added to start the chemical reaction. According to its declaration, Iraq had filled 1,024 bombs and 34 missile warheads with OPA, but the inspectors found 165 empty bombs and 35 "possibly unitary Sarin/Cyclosarin bombs" had also been produced.

In addition, UNSCOM noted a discrepancy of "4,800 rocket-type warheads and 12 aerial bombs" filled with prepared sarin. On her Monday appearance on Larry King Live, the NYT's Judith Miller said in reference to the IED sarin shell that "before 1990, Iraq made approximately 4,800 of these shells," but she seems to be ignorant as to the progression of Iraq's CW development; UNSCOM was generally unconcerned about the 4,800 prepared sarin weapons, since the combination of impurities and acids would have combined to render the weapons unusable over the years -- bad to drink, maybe, but neither a warhead capable of being fired or of creating a toxic plume. We do not know how many 155mm binary GB/GF shells were produced.

Since the 155mm shells were never produced en masse, what does the discovery of this shell mean? First of all, the insurgents who put together this IED were either ignorant of what they had or didn't understand how the shells mixed the chemical. The former scenario is not unlikely, since UNSCOM, upon finding a cache of thousands of mustard-gas shells at Khamisiyah, noted that the shells were in good condition but disordered, and tagged with a largely incomprehensible marking system that did not give any indication of what they were.

Although press reports suggest only a "small" amount of sarin was released, this is only because by exploding the shell, only minimal amounts of the binary chemicals were mixed. Had the shell been fired from an artillery piece, it would have done serious damage.

The discovery of this shell suggests that Iraq lied about its not retaining any chemical weapons. This means either that Iraq had created a store of 155mm shells for offensive purposes, or had maintained a stock for engineering purposes for the days after monitoring ceased. (It is, to be fair, also possible that this was a "rogue" shell that simply didn't get destroyed due to Iraq's byzantine labeling system.)

That's why it's a mistake to downplay this story; it's further proof that Iraq was, shall we say, less than forthcoming in its declarations. On the other hand, there's no solid evidence that the 155mm shells were produced in large quantities, whereas the "crude" rocket and bomb binary weapons are known to have existed in production-run quantities, despite Iraq's attempts at obfuscation and denial. Thus, it's also unlikely (but again possible) that this shell was part of a significant quantity of chemical weapons.

As with many other issues in this war, only time will tell. If more shells appear, the case for war will be strengthened accordingly. But for right now, we have only a hint that Iraq had weapons we have not yet begun to see.