A summary of the Enigma history would be incomplete without an attempt to assess its historical significance, in particular its impact on the fate and outcome of the Second World War. Evaluations of this kind always carry a flavor of subjectivity, so the comments presented below differ fundamentally from the fact- and source-based narrative of the previous chapters. Also, the resulting picture of the role that Enigma decrypts played in the various stages of the war differs from the conclusions presented by earlier commentators. Their views are mostly situated between the extremes set by Harry Hinsley and John Keegan. Harry Hinsley, an active participant in the events with Enigma in the background himself, assessed that without the decrypts provided by Allied codebreakers ‘the war would probably have lasted two or three years, perhaps even four years longer’. Keegan estimated that the decodes shortened the war by only three months. In their absence, the first American nuclear bombs would have fallen not on Japanese cities but on German cities, bringing the war to an end. Any attempt to assess which opinion is closer to the truth, and thus how many months or years of war and how many lives were spared by the work of cryptologists, is situated dangerously close to the judgements quoted above. However, on the basis of the available information, it is possible to assess the extent to which Allied cryptologists, intelligence analysts, military commanders and politicians managed to exploit the opportunities they gained from being able to systematically look into the enemy’s cards during the conflict.