The first use of lethal gas in combat came nine months into World War I, on April 22, 1915. That day, near Ypres, Belgium, the German army opened valves on 5,000 cylinders and sent a cloud of poisonous chlorine drifting into Allied lines. Ever since, civilized nations have struggled to keep this weapon of mass destruction bottled. The threat may someday include potent biological weapons, as well as chemicals, warn some experts.
The United States, for its part, is now on the verge of its most momentous action on chemical warfare in more than a decade. In September, the House of Representatives will hold a final vote on whether to allow US production of new chemical munitions for the first time since the 1960s.
The Reagan administration has been lobbying for such production since 1982. The House has blocked the action in previous years.
But earlier this summer representatives switched position and gave preliminary approval to new chemical weapon construction, if certain restrictions were met. Those restrictions were loosened in a House-Senate conference. The final, mid-September vote will approve or disapprove this change.
The administration is confident, but opponents claim the vote is not a foregone conclusion. ``It'll be closer than the first time we voted on it this year,'' says Rep. John Edward Porter (R) of Illinios, a leading chemical-weapons critic.
The US military years ago decided that the best way to deter the use of chemicals against it was to have a chemical capability of its own.
The current stockpile, manufactured for the most part during the 1950s and '60s, includes some 3 million nerve-gas artillery shells. The US also has obsolete, nerve-gas-filled land mines and rockets, ``Weteye'' chemical bombs, spray tanks that fit no plane now in the US arsenal, and cluster bombs filled with an LSD-like hallucinogen.
These weapons are stored at eight sites in the continental US, one Pacific Island, and one West German facility. Almost half of all chemical munitions are kept at an Army depot in Tooele, Utah.
The military considers only a small portion of these weapons usable, and wants to build modern ``binary'' chemical weapons. Such munitions contain two safe chemicals, which mix and become lethal after the weapon is fired or dropped.
A Chemical Warfare Review Commission, appointed by President Reagan, concluded this June that the US chemical stockpile is more usable than the military thinks. But the panel said modernization of chemical weapons is still needed.
Though current, aging weapons for the most part aren't a safety hazard, says the panel, the new binary weapons would be much safer to handle and transport. In addition, panel members concluded that current weapons have only limited military utility -- many artillery shells are filled with long-lasting agents, though current doctrine calls for front-line use of chemicals that quickly wear off.
``It's not the right stuff, in not the right containers,'' says John Kestor, a former high Pentagon official who served on the commission.
The commission report claims that the Soviet Union has 14 chemical-weapons plants and is researching new biological weapons that might be more lethal than today's chemicals. The Pentagon should be paying more attention to the possible ``chemical and biological threats of the future,'' says the panel's report.
Opponents of new chemical-weapon production claim that the proposed binary shells and bombs are flawed weapons. The current US stockpile, they claim, will be usable into the 1990s.
A current ban on open-air testing of such weapons ensures that any new chemical munition would be sent to the troops untried -- a dangerous proposition, say critics. The proposed new ``Bigeye'' chemical bomb is a particular problem, they say. An October 1984 General Accounting Office report said the complicated ``Bigeye'' was plagued with technical bugs.
Because their citizens would object, America's NATO allies won't allow new chemical weapons to be stored on their territory, say critics. The weapons would have to be airlifted to Europe before they could be used -- reducing their utility in a crisis. John Kestor of the review commission replies that ways could be found to deliver the weapons to Europe quickly.
The US should modernize chemical-weapon defense before it spends cash on new chemical offense, says a House committee aide: A GAO report this spring found that Army-issue chemical protective boots are highly flammable and take 15 minutes to put on.
Finally, critics claim the Soviet chemical threat isn't as ominous as the administration claims -- and that chemical weapons, in general, are good not for attacking troops trained to deal with chemical weapons, but for wiping out civilians. ``If someone could tell me what good these weapons are, I'd be glad to hear it,'' says Harvard biochemist Matthew Meselson.