The decorated former RAF navigator is among the last of a generation which lived through both global conflicts.
During the Second World War, he took part in a daring series of enemy raids including the Battle of Berlin, which claimed the lives of more than 2,000 British crewmen.
Mr Geddes, holder of the DFC (Distinguished Flying Cross), said: “With every year the need for remembrance becomes stronger, as the memories slip from living history.
“It’s hard to understand the impact of the war when you’ve not been involved yourself, but it’s not something I’d ever wish for another generation to encounter.
“All the same, it’s important that people don’t forget just how many people gave their lives, fighting for a better future.”
Mr Geddes was born in London on 7 October 1918 – just a month before the end of the Great War.
He is now a resident at Bupa’s The Lawns care home in Chelmsford, one of many across the country which will host a special service to mark the upcoming centenary for residents less able to attend public services.
After volunteering for the RAF in 1941, Mr Geddes undertook more than 30 operations between 1943 and 1944, regularly returning back to his Yorkshire base RAF Croft in a Halifax bomber riddled with bullet holes.
Recounting one risky mission, he told how his crew were flying over Berlin above dense cloud – when suddenly they noticed enemy search lights shining straight up at him, illuminating the clouds below.
Mr Geddes recalled: “You could see the whole series of Allied bombers flying above the clouds – there must have been hundreds of us flying together.
”Of course, when the enemy lights are on you, you’re anyone’s target.
“They used to say a successful mission was 50 per cent skill and 50 per cent luck – I remember thinking that night was when we were banking on the luck.”
Thankfully, Mr Geddes and his fellow crewmen returned unscathed on that occasion, but others were not so lucky – including Mr Geddes’s former pilot, Flying Officer Funkhouser, who never returned from an operation to Hamburg.
For his valour during the war, Mr Geddes was awarded the DFC by King George VI, marking his efforts in the RAF.
Emily Bingham, activities coordinator at The Lawns, added: “John’s very proud to have fought for his country – his room’s full of pictures from this time and the RAF, along with his medals.
“We arranged a surprise visit from the British Legion and the Royal Air Force Association, and it was fascinating to hear them all recounting stories.
“It’s people like John that help us remember the sacrifices people made, and we’re all very proud of him for sharing his story.”
While serving in the police force in 1939, Mr Geddes met his wife, Florence, who was then working in a biscuit factory.
Mr Geddes proposed in 1940 and the pair married on Christmas Day 1941, going on to have three children together.
Today, Mr Geddes has six grandchildren and five great-grandchildren, though sadly his wife passed away in 1991.
Following the return to peacetime, Mr Geddes spent ten years as a secondary teacher, before returning to his pre-war job in the police force in 1958.
After his retirement in 1973, Mr Geddes was awarded the British Empire Medal by Sir Gerald Walter Robert Templer for his services to the police force.