my understanding......is that the Poles did most of the groundwork, including obtaining info on the machine from Germans as well as reverse engineering an encoding unit (the three wheeled one), and then the Bletchley lot refined all that and cracked the algorithm wide open, and also automated the procedures so messages could be read in a timely manner rather than weeks later.
(,
Tue 31 May 2005, 19:19,
archived)