Helen Taylor Thompson sent coded messages to spies in occupied France during World War II.
“One mistake and someone’s life could have been in danger,” she says.
Ms Taylor Thompson signed the Official Secrets Act aged 19 and was part of what was known as then Prime Minister Winston Churchill’s “secret army”.
She went on to set up Europe’s first Aids hospice and is still working today with her education charity.
Filmed and edited by Jack Slater, produced by Georgina Pearce
What is 100 Women?
BBC 100 Women names 100 influential and inspirational women around the world every year. We create documentaries, features and interviews about their lives, giving more space for stories that put women at the centre.
On 8 March, BBC 100 Women will be showcasing inspirational stories from women in the UK and across the world.