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Look into Bletchley park & the cracking of Enigma...

• mvkel 2y ago
  From Wikipedia: > Nevertheless, there were security leaks. Jock Colville, the Assistant Private Secretary to Winston Churchill, recorded in his diary on 31 July 1941, that the newspaper proprietor Lord Camrose had discovered Ultra and that security leaks "increase in number and seriousness".[59] Without doubt, the most serious of these was that Bletchley Park had been infiltrated by John Cairncross, the notorious Soviet mole and member of the Cambridge Spy Ring, who leaked Ultra material to Moscow.[60]