Originally Posted By: garyW
The FBI defines WMD : http://www.fbi.gov/about-us/investigate/terrorism/wmd/wmd_faqs (the detailed version)

(the brief version)
WMD is often referred to by the collection of modalities that make up the set of weapons: chemical, biological, radiological, nuclear, and explosive (CBRNE). These are weapons that have a relatively large-scale impact on people, property, and/or infrastructure.

Interesting -- the first part of that definition includes:

"Weapons of Mass Destruction (WMD) are defined in US law (18 USC §2332a) as:

“(A) any destructive device as defined in section 921 of this title (i.e. explosive device);"

And according to section 921:

"(4) The term “destructive device” means—

(A) any explosive, incendiary, or poison gas—
(i) bomb,
(ii) grenade,
(iii) rocket having a propellant charge of more than four ounces,
(iv) missile having an explosive or incendiary charge of more than one-quarter ounce,
(v) mine, or
(vi) device similar to any of the devices described in the preceding clauses;

(B) any type of weapon (other than a shotgun or a shotgun shell which the Attorney General finds is generally recognized as particularly suitable for sporting purposes) by whatever name known which will, or which may be readily converted to, expel a projectile by the action of an explosive or other propellant, and which has any barrel with a bore of more than one-half inch in diameter; and

(C) any combination of parts either designed or intended for use in converting any device into any destructive device described in subparagraph (A) or (B) and from which a destructive device may be readily assembled."

So the range goes from anything above a .50 caliber gun to a nuke -- kind of broad definition of "weapon of mass destruction" given the hysteria surrounding the term. I would have thought the definition to be far more limited to weapons having really, really massive and devastating potential (ex: a small nuke vs., like, a hand grenade) ...