The sequence of events was extremely complicated, and naval Enigma played only a minor role in it.
But had the Bismarck sailed just a week later, the story would have been very different.
New developments in Hut 8 were transforming the picture.
This was because the older material was discovered to have powerful implications:
After studying the decyphered traffic of February and April, GC and CS was able to show conclusively that the Germans were keeping weather-ships on station in two areas,
one north of Iceland and the other in mid-Atlantic, and that, though their routine reports were transmitted in weather cypher and were different in outward appearance from Enigma signals, the ships carried the naval Enigma.
This clever analysis of essentially dull material represented a victory for the new men and the new methods, in which Alan had a personal share.
The Admiralty would never have had the time or wit to make the amazing discovery that these vulnerable little weather-ships were supplied with the keys to the Reich.
But they were now prepared to act on the prompting of a civilian department, and plotted a series of captures.