An aggressor would use an agent against which there was a minimal naturally acquired or artificially induced immunity in a target population. A solid immunity is the one effective circumstance whereby attack by a specific agent can be neutralized. It must be remembered, however, that there are many agents for which there is no solid immunity and a partial or low-grade immunity may be broken by an appropriate dose of agent.

There is a broad spectrum of organisms from which selection for a specified military purpose might be made. An enemy might choose an acutely debilitating microorganism, a chronic disease producer or one causing a high rate of lethality.

It is possible that certain mutational forms may be produced such as antibiotic resistant strains. Mutants may also be developed with changes in biochemical properties that are of importance in identification. All of these considerations are of critical importance in considering defense and medical management.

Biological agents are, of course, highly host specific. They do not destroy physical structures as is true of high explosives. This may be of overriding importance in considering military objectives.

The question of epidemic disease merits some discussion. Only a limited effort has been devoted to this problem. Some of those who question the value of BW have assumed that the only potential would be in the establishment of epidemics. They then point out that with our present lack of knowledge of all the factors concerned in the rise and fall of epidemics, it is unlikely that a planned episode could be initiated. They argue further (and somewhat contradictorily) that our knowledge and resources in preventive medicine would make it possible to control such an outbreak of disease. this is why this approach to BW defense has not been given major attention.