The Pentagon is exploring new ways of attacking underground sites containing chemical or biological weapons, including the idea of a deep-penetrating bomb designed not to blow up a target, but to seal it off with an impenetrable substance like sticky foam.
Pentagon officials stress it is only a concept. No sticky foam bomb exists nor is the weapon under actual development.
But the idea is a compelling one, neutralizing an underground chemical or biological weapons site rather than simply destroying it.
Stephen Younger, director of the Defense Threat Reduction Agency, said such a foam bomb could minimize the risk of spreading poisonous gas or germs that might be released by a conventional explosion. Such a release could threaten soldiers as well as civilians.
Speaking this week to a group of reporters, Mr. Younger said another concept under study is a weapon that would disperse flammable material on a chemical or biological site, triggering an intense fire to incinerate any dangerous agents.
Pentagon officials recently developed and produced a thermobaric or heat and pressure bomb that could be the precursor for such a weapon.
This bomb was used for first time in combat last March against cave complexes in which al-Qaida and Taleban fighters had taken refuge in the Gardez region of Afghanistan.
Military officials have said the challenge in developing an effective anti-chemical or biological weapon will be the need for it to be effective against a variety of targets and agents.
The different types of target structures range from above-ground to deeply buried and the different types of agents include dry spores, vegetative cells, viruses, toxins and chemicals.
Defense officials have said another concept under consideration is arming intercontinental ballistic missiles, ICBM's, with conventional warheads instead of nuclear ones to strike targets like other missiles that might be armed with a biological weapon.
Such a missile could be used, for example, if intelligence sources detected the imminent launch of the biological weapon but no aircraft or troops were nearby who could strike quickly enough to prevent the weapon's launch. The ICBM could be there within minutes.
However, officials say there are a number of issues that must be dealt with if the ICBM idea is to go forward. One critical issue would be resolving the fear factor among other countries who might detect the ICBM's launch and view it as signaling the start of a nuclear war.