The morality of weapons research.

I ask whether weapons research is ever justified. Weapons research is identified as the business of the engineer. It is argued that the engineer has responsibility for the uses to which the tools that he designs can be put, and that responsibility extends to the use of weapons. It is maintained that there are no inherently defensive weapons, and hence there is no such thing as 'defensive' weapons research. The issue then is what responsibilities as a professional the engineer has in regard to such research. An account is given to ground the injunction not to provide the means to harm as a duty for the engineers. This account is not, however, absolutist, and as such it allows justifiable exceptions. The answer to my question is thus not that weapons research is never justified but there must be a strong assurance that the results will only be used as a just means in a just cause.