It was the battle that changed the course of the first world war, ushering in the collapse of the German army on the western front and delivering the armistice some 100 days later. Yet the battle of Amiens in France, the first day of which was said by Gen Erich Ludendorff to have been Germany’s blackest, has faded from public memory, left in the shadows by the horrors of the Somme and Passchendaele.

At Amiens cathedral on Wednesday, Prince William and the British prime minister, Theresa May, will join 3,000 members of the public, including descendants of those who fought in the four-day assault, 100 years to the day of the start of the battle that brought the war out of the trenches at a cost of 46,000 allied casualties and as many as 75,000 German losses, including those taken prisoner.

May will read an extract from the war memoirs of the then British prime minister, David Lloyd George. The former German president Joachim Gauck is to read the poem After a Bad Dream 1918, by Gerrit Engelke, a soldier and writer, sometimes referred to as the German Wilfred Owen. Both men died in the last weeks before the Armistice.

Beginning at 4.20am on 8 August 1918, Allied aircraft, tanks and infantry took their cue from 900 heavy guns to sweep through the front with such speed that some German officers were captured while eating their breakfast.

Among those killed on that first morning was the great-great-grandfather of 18-year-old Amiens Fowler: the Canadian soldier Frederick Spratlin, 36, was shot as he tended to the wounds of another man. Fowler was named after the French city close to where her ancestor was killed.

Amiens and Michelle Fowler. Photograph: Family archive

“When I was little, I didn’t appreciate the value of my name; it was the name that no one knew how to pronounce,” said Fowler, a student. “But now I take time to tell them the story. I’m proud my name carries his memory, and I get to tell people about him.”

L/Cpl Spratlin, a stretcher-bearer already decorated for his bravery, was shot in the chest on the first morning of the attack, after his battalion, moving through heavy fog, met a well-manned machine-gun post.

“He had just attended to the wounds of one man and was going to the assistance of another when he was shot in the chest,” wrote Capt Alexander MacDonald to Spratlin’s parents. “I was beside him at the time and in spite of immediate attention the wound was so serious that instant death resulted.”

Frederick Spratlin with his wife and children. Photograph: Fowler family archive

Some 10 years after the war, MacDonald sought out Spratlin’s youngest daughter, Florence – Amiens’ great-grandmother – to express his continued sorrow. Florence, who died in 1996, was about seven years old when she was told of her father’s death.

One of the few of Spratlin’s possessions to survive was his annotated Bible, a gift from his daughter Janet, that was handed to him a week before he left Canada aboard the RMS Empress of Britain as a member of the 75th Battalion, Canadian Expeditionary Force.

Some 90 years on, the New Testament’s soft leather cover is still bowed, indicating its former home in Spratlin’s breast pocket. It is believed he would read extracts to those he was seeking to save, or could not. His grieving wife, Mary Ethel, never remarried.

Spratlin’s bible. Photograph: Fowler family archive

Michelle Fowler, 47, Amiens’ mother, said Florence used to talk about Spratlin almost every day. “One of the last memories that she had of him was him getting on a street car, maybe to work, but that was her last active memory, of saying goodbye to him.

“And she had the somewhat typical memory of the Toronto city kids of those who went to the first world war: the boy on the bicycle carrying the telegraph. She was outside playing, and there was one other boy on the street whose father was at war, and when the boy cycled past that boy’s house, she knew her father had died.”

Fowler, a historian, was inspired by the story of her relative, and a great uncle who died on Juno beach in Normandy in the second world war. “It doesn’t seem like 100 years ago because his memory was kept alive by her. He was always part of our life so to speak.

“He annotated the Bible and it appears from the front cover that there were passages that gave him comfort during certain times. Different aspects of the war were labelled – sentry duty, officers – and had little passages by them. He had labelled out the war.

“Canada doesn’t talk about Amiens, particularly, but we talk of the last 100 days of the war being more a glorious chapter – and that started with Amiens.”

Remembering the war

1,634 babies were given names related to the first world war between 1914-1919 in England and Wales.

901 babies were given the name Verdun, making it the most popular.

166 babies were called Kitchener and 11 were named Haig.

120 babies were called Victory, 107 of whom were born at the end of the war. 84 babies were named Peace.

Almost all children named Armistice were born on 11 November 1918, or within a few weeks of this date.

At least 10 babies were called Passchendaele.

15 babies were named after the Somme.

71 babies were called Ypres.

Three babies were named Amiens.

Source: UK Department for Digital, Culture, Media and Sport