I desparately try not to become a member of a "conspiracy theory" - but I certainly do NOT believe a lot of what is written about the immediate post-war nuclear (or rather then "atomic") relations between the UK and USA.
It is inconceivable to me that the MacMahon Act went through without strong representations from both the British Ambassador to the US and from the British government directly. The idea that Trueman never realised that the Act went directly against the Quebec Agreement is just plain silly.
Likewise the idea that somehow a magic wand was waved in 1958 I also find suspicious (but I can't pin that down to anything).
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