Some of those recruited came from Oxford and Cambridge and others on personal recommendations or from the armed forces but recruitment wasn't always so conventional. A crossword competition in one of the daily newspapers identified those who could complete a crossword in a short time and they were called for interview.
It wasn't only the cryptographers' work that was special about Bletchley Park though. The creation of the bombe - a mechanical device developed to break the German Enigma code machine by Alan Turing, Gordon Welchman and Harold Keen building on information received from the Polish Cypher Bureau shortly before war broke out - led eventually to the creation of automatic machines to deal with the volume of encrypted messages and from them to the creation by Tommy Powers and his team of Colossus, credited as the world's first digital electronic computer that could be programmed, in 1943. Ten of these were in use by the end of the war. While Colossus was efficient at the task for which it was designed it was limited and, sadly, because of the secrecy surrounding the machines and the work of the cryptographers, The government ordered the dismantling all of the Colossus machines and all drawings and notes were supposed to be destroyed.
There's a but, though, luckily for us. Despite all the efforts to destroy any plans or parts, enough remnants remained in engineers' notebooks and in the US to enable a reconstruction which is now on display at The National Museum of Computing at Bletchley Park.
Bletchley Park and those who worked there are no longer hidden in secrecy and Bletchley Park, run by the Bletchley Park Trust, is now open to the public, housing The National Museum of Computing and a number of other exhibits.