A major ENIGMA weakness was created when some fool decided it was a good idea to not allow any single encrypted character to be encrypted by the same character in the pseudo-randomly generated key... a character of the plaintext could not be encrypted by the same character in the key.. plaintext A would never correspond to A in the key sequence... a truly moronic mistake that gave Bletchley Park a great gift.
General Erich Fellgiebel was responsible for German military signals in WW II. He pushed for the adoption of Enigma. As a plotter against Hitler, he was tortured and executed without ever revealing the names of any coconspirators. As a man of exceptional intelligence and discipline, Fellgiebel might also have deliberately introduced or tolerated flaws in Enigma security as a way to help defeat Hitler. In any event, it is known that Fellgiebel repeatedly suppressed investigations that strongly supported suspicions that Enigma had been compromised.