St John Ambulance cadets joined with fellow uniformed groups to commemorate the work of volunteers in WWI.
The young volunteers from Harrow joined others from across London at the Royal Hospital Chelsea memorial service to mark the start of the Great War 100 years ago.
During the war more than 45,000 St John Ambulance volunteers provided vital first aid and care in military hospitals as part of the Voluntary Aid Detachments.
After the ceremony the cadets were shown first aid techniques and materials available in 1914 and were able compare them with modern standards.
Kevin Munday from St John Ambulance said: "It was a real honour to be able to take part in such a fitting tribute to Great War Volunteers.
"It's really important for our young people to be connected with their history and this occasion was an opportunity for them to hear the stories of the unsung heroes of the First World War."