Gwendoline Page was 14 years old when World War II broke out. A pupil at Queen Elizabeth School for Girls in Barnet, she lived in Borehamwood, which was on the way to and from several Nazi targets in London.

Gwendoline joined the Women’s Royal Navy Service (WRNS or ‘Wrens’) at the age of 18. She was annoyed to be sent to rural Bletchley Park in Buckinghamshire, instead of to a port.

But she was to become part of one of the most important aspects of the war effort.

At the time, scientists at Bletchley Park were deducting how to crack the Nazi’s Enigma machine. This enabled them to decode enemy signals and helped to turn the war in the Allies’ favour.

It has been stated that intelligence produced at Bletchley shortened the war by two to four years, and that without it the outcome of the war would have been uncertain.

In January, 1945, at the peak of codebreaking efforts, around 10,000 personnel worked at Bletchley, 75% of whom were women.

Many of these women came from middle-class backgrounds and held degrees in mathematics, physics or engineering. They were given entry into STEM programs due to the lack of men, who had been sent to war.

After initial training at the Inter-Service Special Intelligence School, staff worked a six day week, rotating through three shifts. The irregular hours affected workers’ health and social life. The work was tedious and demanded intense concentration.

Properly used, the German Enigma cipher should have been unbreakable. But flaws in German cryptographic procedures and poor discipline among the personnel carrying them out created vulnerabilities that made Bletchley’s attacks just barely feasible.

These vulnerabilities could have been remedied by simple improvements in enemy procedures, so it was vital that they knew nothing of what the staff at Bletchley were doing. Thus the intelligence that Bletchley produced was considered ‘Ultra Secret’ – higher even than the highest classification of ‘Most Secret’.

Gwendoline was lucky enough to be too short to work in what the Wrens called ‘The Hellhole’, a room containing a huge machine which was used to decipher enemy codes, and was a hot and deeply unpleasant place to work. It had no windows because they could not risk people looking inside, and neither was there any air conditioning.

Gwendoline worked at the Naval Section at Bletchley Park, indexing U-boat signals. Indexing the U-boats built up a complete picture of the vessel, including who the Commander was. Tracking where U-boats were and destroying them before they hit crucial supply vessels was of paramount importance.

Gwendoline was not able to tell her parents about her efforts during the war because of the Official Secrets Act. Staff were unable to speak of their duties until 30 years after the end of the war. Many relatives never knew that a child, spouse or parent had contributed to secret war work. Her parents died before she was able to break her silence.

After the war was over in Europe, Gwendoline took part in the Pacific campaign, before moving back to Borehamwood. She married in the Baptist Church in September, 1946.

She began her teaching career at Furzehill School. When she retired, she took up writing about her lifetime of experiences and her books include We Kept the Secret and They Listened in Secret.

The site at Bletchley Park passed through a succession of hands and saw a number of uses, including as a teacher-training college. By 1991, the site was nearly empty and the buildings were at risk of demolition for redevelopment.

In February, 1992, the Milton Keynes Borough Council declared most of Bletchley Park a conservation area, and the Bletchley Park Trust was formed to maintain the site as a museum. It opened to visitors in 1993.

2014 saw the completion of an £8 million restoration project, which was marked by a visit from Catherine, Duchess of Cambridge. The Duchess’ paternal grandmother, Valerie, and Valerie’s twin sister, Mary, both worked at Bletchley Park during the war.