Mrs May laid a wreath at the service in Amiens Cathedral

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Mrs May gave the Prince a respectful low curtsey as they met on the steps of the 13th-century Amiens Cathedral. The breakthrough battle’s surprise attack was launched in thick fog on August 8, 1918 and triggered the “100 Days Offensive” that defeated the Kaiser and brought the Armistice of November 11, 1918. But though France also took part in the battle, President Emmanuel Macron was represented by armed forces minister Florence Parly. Other dignitaries included former German president Joachim Gauck. The four-day battle saw a revolutionary combination of Allied forces – tanks, warplanes, artillery and infantry – which turned the tide on the Germans. Prince William, who wore an Irish Guards tie and performed a reading to the 2,000 inside the cathedral while 1,200 watched outside, said: “The Battle of Amiens brought the Allies hope and optimism after four long years of bloodshed and stalemate.

Armed Forces chief Sir Nick

The effect of the victory was moral and not territorial. It revealed to friend and foe alike the breakdown of the German power of resistance. David Lloyd George

“The Battle of Amiens was a historic point in the conflict which had wreaked unparalleled levels of havoc, devastation and death during the preceding four years. A conflict which had touched people in almost every part of the world and to which there seemed no end. “Yet three months after the battle the Armistice was signed and at the eleventh hour of the eleventh day of the eleventh month the guns fell silent.” Mrs May, who interrupted her summer holidays to attend, paid tribute to the “courage, bravery and skill” of troops who fought in the Battle of Amiens. And she told how the battle and the subsequent 100 Days Offensive used revolutionary tactics to break the deadlock on the Western front. She said: “Following the success of Allied forces at the second Battle of the Marne in the preceding weeks, the Allies adopted a number of tactics at the Battle of Amiens which continued that success: secrecy and surprise, the use of targeted air power by the RAF, the phasing of the attack to allow for rest and consolidation and, perhaps most importantly of all, the coordination of Allied troops working together in coalition.”

Yet in a reading in the Cathedral, Mrs May revealed that at first the Allies had not realised the significance of the breakthrough. Quoting the memoirs of wartime premier David Lloyd George, she said: “The fact of the matter was that the British Army itself did not realise the extent and effect of their triumph they had won that day. “The effect of the victory was moral and not territorial. It revealed to friend and foe alike the breakdown of the German power of resistance. “More finally even than by the French counter-offensive of July 18 were the Germans driven by the British stroke of August 8 to realise that all hope of victory had passed.”

Sarah Clarke-Feltham paid tribute to her grandfather George Clarke – and his real life war horse.