Once they had started breaking Enigma in the Cottage, using Jeffreys sheets, Welchman, who had quite independently thought of the sheet method, realised that a massive break into the German Enigma traffic could be achieved. This arose from the German key system for Enigma.
The Enigma settings were changed every day at midnight, so for 24 hours everyone on a particular communications net were on the same Enigma settings. Thus, Welchman realised, if just one Enigma message could be broken and the base settings found, all the traffic for that whole 24 hour period could just be decrypted.
Welchman thus saw that a rapid increase in manpower would be required at Bletchley Park and that the organisational structures had to be put in place immediately to handle the intelligence material. He put together a paper on his proposed structure and took it the Deputy Director, Commander Travis.
Travis immediately saw the importance of it and gave it his enthusiastic backing.
In a very short time it was being implemented. Welchman said later that this was probably his greatest contribution to the War effort.