I am writing a paper on the development of the doctrine of preemptive
self-defense. In the last couple of weeks I read a quote written by an
American state official in the 1940s (I think). The problem is I can't
remember where I read the quote or what it said exactly other than the
following:
It identified that the original doctrine of self-defense had to be
updated inlight of new WMD. It didn't actually use the term 'WMD' as i
think this is a relatively modern term; I think it used 'the atom
bomb'. I think it was Secretary of State Cordell Hull in 1945 but it
may have been a different official a little earlier or even a
different official a little later.
The exact quote and source would be much appreciated.

I wasn't able to find an appropriate quote from the 1940s, but I came
across this interesting quote from the Eisenhower era:

"Given the power of modern weapons, it should be the task of our
strategic doctrine to create alternatives less cataclysmic than a
thermonuclear holocaust."

Henry Kissinger, Nuclear Weapons and Foreign Policy (New York: Harper,
1957), p. 19.

http://carlisle-www.army.mil/usawc/Parameters/05summer/laver.htm