A machine called the "cryptologic bomb" (Polish: "bomba kryptologiczna") had been produced by the Polish codebreakers in their successful breaking of Enigma before 1939. It was, however, useful only as long as the Germans continued with particular weaknesses in operating procedure, which they gradually tightened up, so that the Polish success rate diminished dramatically. Alan Turing designed the British bombe on a more general principle, the assumption of the presence of text, called a "crib", that cryptanalysts could predict was likely to be present at a defined point in the message. This technique is termed a "known plaintext attack" and had been used to a limited extent by the Poles, e.g., the Germans' use of "ANX" — German for "To," followed by "X" as a spacer.