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.