On dosage level, my recollection is that we worked on a WED of 75 roentgen for purposes of estimating the worst case usefulness of rescue staff - or the potential for use of various routes for evacuation.
We understood at the time that the armed forces uses the same or similar values; I recall quite a lot of discussion amongst the scientists - almost all the staff were research scientists, some impressively eminent and well known (spending time listening to them was a major upside for an impressionable youth!) - as to how the limits had been derived, and what the experimental evidence backing it up was. The suspicion was that medical tests after Hiroshima and Nagasaki were probably important, plus much extrapolation given the uncontrolled nature of the 'experimental conditions' !
Form what I have seen much more recently, those dosages would have dramatically reduced life expectancy and lifespan, to say the least. Hmm.