As I have developed this paper, I have been fortunate to have been able to present some of the ideas that it contains at seminars and conferences around the world, and to listen to perspectives from experts hailing from all of the world's nuclear-armed states. Paul Schulte has been a frequent companion at many of these events, and I learnt much from our frequent discussions and jointly written projects, as well as from his persuasive comments on this paper in draft form. Shashank Joshi, my RUSI colleague, took time away from writing his own monograph on Iran's nuclear programme to provide detailed feedback. I owe a particular and heartfelt debt to James Acton for his thoughtful, detailed and incisive comments on an earlier draft. James has already written several excellent papers on deterrence at low numbers, all of which provided inspiration for this work.
I would particularly like to thank Ashlee Godwin and Adrian Johnson for their tireless editorial efforts. The paper would have been much poorer without their insistence on clarity and conciseness.
This paper was made possible as a result of the financial support of the Nuclear Threat Initiative in Washington, DC, which has consistently supported RUSI's nuclear work for several years.