A century ago, on November 20 Britain was at war with Germany and it was on this day that the Battle of Cambrai took place.
The aim of this offensive was to attack the Hindenburg Line, the last and strongest of the German army's defences on the Western Front.
This famous assault marked the first large-scale use of tanks for a military attack. The Royal Tank Regiment commemorates the anniversary of the battle annually on Cambrai Day, 20 November.
It is the most important day in the Regimental calendar and is commemorated wherever its troops find themselves, from the battlefields of the Second World War to the deserts of Afghanistan to their current barracks in Tidworth, Wiltshire.
The Battle of Cambrai lasted until December 6 1917. It was the first time that tanks had been used in significant numbers, with more than 450 deployed.
The battle is also widely recognised as the first time that UK and US soldiers fought and died together in conflict, as US Army engineers were attached to support the British attack.
Soldiers from The Royal Tank Regiment based in Tidworth on Salisbury Plain have taken part in a special parade and drumhead service to mark the 100th anniversary of this significant event which forms such a large part of their history.
Forces Radio BFBS Salisbury's Chris Sturgess went along to the service.