Butcher is the author of "The Origins of the Russell-Einstein Manifesto,"a splendid essay detailing the historical development of the manifesto up through the first Pugwash conferance. It is quite informative.
She also pointed me towards a recent op-ed piece by Joseph Rotblat, the last remaining signatory of the Russell-Einstein Manifesto. Rotblat frames the significance of the manifesto poignantly:
Fifty years ago we wrote: "We have to learn to think in a new way. We have to learn to ask ourselves, not what steps can be taken to give military victory to whatever group we prefer, for there no longer are such steps; the question we have to ask ourselves is: what steps can be taken to prevent a military contest of which the issue must be disastrous to all parties?" That question is as relevant today as it was in 1955. So is the manifesto's admonition: "Remember your humanity, and forget the rest."