Jerry Roberts, who has died aged 93, was one of the leading Bletchley Park codebreakers working on the Fish teleprinter messages sent between Hitler and his generals which revealed that the Germans had been fooled by British deception, so ensuring the success of the D-day landings. Roberts worked in the Testery at the Buckinghamshire estate, where communications between Field Marshal Gerd von Rundstedt, the German commander in France, and Hitler were deciphered. The codebreakers named the teleprinter ciphers Fish, and the link between Von Rundstedt and Hitler was known as Jellyfish.
"Many messages were signed by top field marshals like Von Rundstedt," Roberts wrote in Colossus: Bletchley Park's Greatest Secret (2006). "Occasionally there were messages signed by Hitler himself. I can remember deciphering at least one message he called himself: 'Adolf Hitler, Führer'."