What clues did Bletchley Park code breakers use to start a Bombe search?

To initiate a Bombe search, Bletchley Park code breakers relied on a technique involving "cribs".12

A crib was a guess or an educated prediction of a specific portion of the plaintext within an intercepted Enigma message, such as a recurring weather report or a standard operational phrase. By comparing the patterns of the encrypted ciphertext against this known or suspected plaintext, cryptanalysts could identify potential settings for the machine.12

This method was particularly effective because it utilized the fact that no letter in an Enigma message was ever encoded as itself, providing a consistent logical constraint for the Bombe to exploit. Once a crib was established, the Bombe would search through the possible scrambler configurations to find a match that turned the coded letters into the hypothesized German text.12