As far as I see, neither of the examples you linked provides any evidence that in 1939 it was incorrect to consider a British government assassination plot against Hitler as wildly implausible. The Oster conspiracy was an internal German plot, and the Foxley plan was just a proposal that was never approved nor carried out (and even as such, it occurred only after five years of a total war in which nearly all other centuries-old conventions of civilized warfare had been discarded -- a world very different from the one five years earlier).

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