The Duke of Cambridge and the prime minister are attending commemorations in northern France later to mark the centenary of the Battle of Amiens – the beginning of the end of World War One.
Prince William and Theresa May will give readings at a service at Amiens Cathedral and lay wreaths.
They will also meet descendants of the soldiers who fought.
The British-commanded Fourth Army was involved in the battle, heralding the start of the Hundred Days offensive.
General Sir Henry Rawlinson had learnt the lessons of the bloody Somme offensive and employed improved tactics and new equipment.
More than 500 UK tanks were deployed, alongside 1,900 British and French aircraft, and more than 2,000 guns from the Royal Artillery.
A string of military victories by combined air and land forces from Britain, Australia, Canada, France, and the US followed, leading to the surrender of German forces and the end of the conflict on 11 November 1918.
Armed Forces Minister Mark Lancaster and Chief of the Defence Staff General, Sir Nick Carter, will also attend the service.
General Sir Nick Carter said the Battle of Amiens was a “remarkable achievement… moulding a new citizen-based force into a very accomplished fighting force, against a backdrop of rapid technological change”.