If the German operators always worked correctly, no two messages would have the same start position of the wheels. However, mistakes were made. They helped the British codebreakers. On 30 August 1941 two versions of the same message, which was nearly 4,000 characters long, were sent with the same wheel start positions. This mistake was very useful to the research codebreakers. A codebreaker called John Tiltman was able to get the keystream from these messages.