Mavis Batey

Mavis Batey, who has died aged 92, was a Bletchley Park codebreaker whose work on Nazi messages played a pivotal role in the Second World War. Some historians have asserted that the work of Batey and others shortened the war by two years.

She was famous for a number of important breakthroughs, including the decrypting of a message that led to the Royal Navy's victory over the Italians at Matapan in 1941. She also broke the codes of the Abwehr, or German military intelligence, which helped ensure the success of the D-Day landings.

She was born Mavis Lilian Lever in Dulwich, the daughter of a postal worker and a seamstress, and studied German at University College London. When war broke out, she volunteered to work as a nurse but was told that her fluency in German could be put to good use.

At first, Mrs Batey was excited at the prospect. "I thought, great, this is going to be an interesting job, Mata Hari, seducing Prussian officers. But I don't think either my legs or my German were good enough because they sent me to the Government Code and Cipher School."

The school was based, unpromisingly, in huts at Bletchley Park, and it was there that Mrs Batey was put to work cracking codes under the famous Dilly Knox. She was still only 19 years old.

One of her most famous breakthroughs came in March 1941 when she decoded a message from the Italian navy which read "Today's the day minus three". It clearly suggested a major attack and the next message Mrs Batey decoded confirmed the details, including the battle plan, the number of warships involved and the location of the attack against a Royal Navy convoy.

It was a major coup for Bletchley and the information was sent immediately to the Royal Navy who were able to anticipate the Italians' movements and inflict a major defeat on them at the Battle of Cape Matapan, off Greece. Five Italian warships were destroyed.

Mrs Batey's success with the Abwehr codes came later in 1941 when, with Knox and another colleague Margaret Rock, she worked on breaking the Enigma machine used by the Germans.

The team was eventually successful which meant the British could not only read the Abwehr messages, they could see that the Germans were falling for phoney intelligence designed to confuse them.

This meant the British were able to trick the Germans into believing the Allies were planning to land Pas de Calais rather than Normandy.

Hitler then fortified his troops in the wrong area, helping to secure the success of the D-Day assault on June 6, 1944.

Historian Michael Smith said Mavis Batey was the last of the great 'break-in' experts who broke ciphers that no one else could work out. "She was a remarkable woman," he said, "and someone I will never forget, nor will anyone who ever met her."

After the war, she established a reputation as a garden historian after restoring her garden in Oxford, where her husband, Keith Batey - also a codebreaker at Bletchley - was chief financial officer.

She always remained modest about her achievements, which were dramatised in the movie Enigma with Kate Winslet playing Mrs Batey.

"I was just part of a team," she said. "We were all part of a team. The heroes were the chaps who were fighting on D-Day."

She is survived by two daughters and a son. Keith Batey died in 2010.