20th November, 1968
Dear Matt
It was really most kind of you to send me not only the articles but also your very long and helpful letter.  Unfortunately, it did not arrive before I gave the lecture, so I only made a few guarded comments in it about biological warfare.  As far as I remember I mentioned that the major powers did not appear to think that biological weapons were much good.  I also said that I would personally be reluctant to work on them.
Since then I have digested what you sent me and I would have replied to your comments sooner had I been able to make up my mind about them.  I do not have much doubt that it would be foolish for this country to stockpile such weapons, for all the reasons you give in your letter.  It also seems sensible for countries like Sweden and Britain to do a certain amount of research of a more or less defensive nature.  Most of this need not be secret, but I have been unable to decide whether I agree with those people who feel that none of it should be secret.  It would take too long to go over all the factors involved here, but in brief the main points are:-
(1) Much as I should be I am not a pacifist because I feel there are a small number of circumstances in which a nation should fend for itself.
(2) Under another threat, comparable to the Nazi threat, I should feel personally obliged to join in a defensive war effort.
(3) If there is some finite prospect of this happening in the future it would be foolish not to engage in some sort of defensive research work, and it might be foolish to let such a dangerous potential enemy know everything that one was studying.
Of course, against this it can be urged that the risk is so small that it would be better to have everything in the open.  The only thing that emerges, as far as I am concerned, is that the smaller nations should make every effort to engage in co-operative defense research, and that at least a greater part of this should not be secret.
One final point, although I agree that at the present time biological weapons look very poor weapons, I am not convinced that this situation will necessarily always remain the same.  I think what really worries me is the frightening possibility that somebody might come up with a good biological weapon.  It is for this reason that I should be extremely reluctant to have, say, you and Sydney work on the development of new biological weapons!
I am afraid you will find all these tentative thoughts rather naive but I will continue to think about the problem.  I hope we can have a thorough discussion about it next time we meet.
F.H.C. Crick