[bendykstra]

Just as during WWII, during WWI, the British had a very sophisticated interception and decryption program[1]. Its capabilities were also kept secret for long after the war and the Germans remained largely ignorant of how thoroughly their codes had been broken. I think if the work during WWI had been revealed earlier, the Germans would have been more careful and would have avoided repeating some of the mistakes of WWI. It was shown to be a wise policy after WWI, so I'm not surprised that they continued it after WWII, especially with the start of the Cold War.

1. https://en.wikipedia.org/wiki/Room_40

[danielam]

I can't speak about the relative sophistication of British cryptanalysis during WWI, but Bletchley owed much of its sophistication to the Poles. The Polish Cipher Bureau was responsible for bringing mathematical and computational techniques into cryptanalysis while the French and the British were still largely employing linguistic analysis. Few realize that the Enigma was actually broken and reverse engineered by the Cipher Bureau before two new rotors were added by the Germans less than a year before the War, or that Turing's bombe was developed from Rejewski's bomba.

[richieb]

The Poles certainly got the ball rolling (see http://www.codesandciphers.org.uk/virtualbp/poles/poles.htm), but the organization at Bletchley Park took decryption and analysis of Enigma traffic to an industrial scale. By the end of war Bletchley employed around 10,000 people. See Alan Turing's and Gordon Welchman's biographies for more details.