The use of radiological warfare is becoming a viable possibility as more countries are gaining the technology and materials needed for radioactive weaponry. Radiological warfare, which is radioactivity (excluding nuclear bombs) as a means of warfare, could be used on the defensive (to make an area impassable for enemy troops, to halt an armoured attack, to inhibit a river crossing, or to close mountain pass); or on the offensive (to force evacuation from cities, industrial areas and communication centres, thus a wreaking havoc with the economy and fighting potential of the country attacked); or it could simply be used to kill a large number of people. Radioactive elements such as radioactive strontium could be used to poison food or water of an enemy force.
Doctors who carried out some of the government radiation experiments on unwitting citizens of the USA during the Cold War were also studying potential military application of radiological poisons. After feeding rats radioactive elements, in the 1940's one doctor secretly used three terminally ill human patients as experimental subjects to test lethal doses of plutonium. There is fragmentary evidence to suggest that other radioactive substances (including polonium, americium and radium) were injected into other, as yet unidentified subjects. One result of his work was to suggest to the military the use of radioactive smoke (fission product aerosols) as a killing agent for urban populations. (He sought healthy human volunteers to inhale near-lethal doses of radioactive aerosols, but found none. Having received an Atomic Energy Citation for "inspired, effective and pioneering leadership", he died in 1957, aged 49, of a rare form of leukaemia almost certainly caused by exposure to radiation).