(CNN)On the banks of France's Arve river, the horse the Germans could not kill faced his most dangerous mission yet.
World War One: 'The horse the Germans could not kill'
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The star-foreheaded Warrior, who arrived on the Western Front in August 1914, had survived four years of shells and bullets, come through the horrors of Ypres, the Somme and Passchendaele, and was now about to lead one of the last great cavalry charges in history.
In the saddle was General Jack Seely, a flamboyant aristocrat and politician. The pair advanced, galloping at speed for half a mile on muddy terrain before mounting a hill.
Behind the thoroughbred on that morning of March 30, 1918, were 1,000 horses of the Canadian Cavalry; a brigade of cowboys, Mounties, clerks, and Americans. Squadron after squadron followed Seely and Warrior, supported by the Royal Flying Corps which dropped 190 bombs.
Morning turned into a rainy afternoon, then light faded. Warrior survived, as did most of Seely's command, and Moreuil Wood was taken by the Allies, bringing German advancement to a halt.
"Warrior was the lucky one," Brough Scott, journalist and grandson and biographer of Seely, tells CNN.
"My grandfather was unbelievably lucky with Warrior. One moment he and another horse were standing together, the horses touching noses while other people marched across a bridge, and there was a sniper and the horse next to him was shot dead."
General Seely once said of Warrior: "I have seen him, even when a shell has burst within a few feet, stand still without a tremor -- just turn his head and, unconcerned, look at the smoke of the burst."
Warrior returned home to the Isle of Wight in 1918, living on the island off the south coast of England with the Seely family until his death aged 33. Dubbed "the horse the Germans can't kill," by Canadian soldiers, Warrior's obituary would appear in English newspapers The Times and Evening Standard and, in 2014, he posthumously received the Honorary PDSA Dickin Medal, known as the "animal Victoria Cross."
He is still remembered, still admired. Steven Spielberg, director of War Horse, said during the release of his Oscar-nominated film: "Warrior is an extraordinary example of the resilience, strength, and profound contribution that horses made to the Great War."
The First World War was a global conflict that defined a century. A four-year battle fought in the fields, the bloodiest in European history, a war which was supposed to end all wars. Sacrifices were made which should never be forgotten, especially the contribution of the stoically silent volunteers regarded as the ultimate war machines.
Horses were the backbone of the Allies' effort, essential to what ultimately would be victory.
The British Army alone deployed more than a million horses and mules, buying over 617,000 from the US and Canada. Indeed, according to the National Army Museum, Britain sent more hay and oats by weight than ammunition to France.
When the war began in 1914, the British Army possessed just 25,000 horses -- within 12 days 140,000 had been purchased.
"The British Army had a very organized system in 1914 to sign horses up for the cavalry because they were aware that they would need horses badly," says Scott.
"By 1915, 16,000 horses had come from Tennessee, 2,000 from Uruguay. It was horses everywhere.
"We can be too sentimental, but what has been obvious, I think, and particularly the reaction I've had about Warrior, because horses can't speak there's a noble, uncomplaining, inspirational stoicism about the horse going about its work.
"It doesn't have a choice, but will go and work for you and, in many cases, die for you."
Immense resources were invested in the horses which had four main roles: Supply horses and mules were used to move ammunition, general supplies and ambulances, riding horses were ridden by soldiers, gun horses pulled artillery pieces and cavalry horses were used in battle. Britain's Remount Department alone spent about $3.9 billion in today's money on purchasing, training and delivering horses and mules to the front.
"A lot of the times they were standing in makeshift shelters in the fields and things were pretty brutal," explains Scott.
"Horses are bigger targets and you can't make them lie down. They were going all the time. Riding horses you're a big target."
As well as being instrumental to the war effort, for the men in battle the war horses were inspirational figures, says Scott, acting as morale boosters in the darkest of times.
"My grandfather was a flamboyant figure, he would be up near the front when they were parading and marching and very much not hiding and for the troops behind him, seeing the horse up there in front was something they found really inspirational and totemic, he was the ultimate mascot," says Scott of Warrior.
"My grandfather would say that when he rode up to the troops, they were saying 'here comes Warrior.' With a horse, you can go up to it and pat it and say 'good chap.' There's no doubt for those cavalrymen their morale was kept up. Thinking about somebody else is helpful, no question."
Horses were, of course, part of everyday life in the early part of the 19th century.
"Today we forget how much horses were used," Emma Mawdsley, an art historian curating an exhibition at the National Army Museum in London on a collection by British war artist Sir Alfred Munnings, one of England's most celebrated equine painters.
"The success of the British war effort was totally dependent on horses.
"A new type of war saw men live for months in trenches instead of fighting on the move. Often the mud was so thick motor vehicles could not drive through it. It was left to horses to pull the large artillery guns and ambulances, and bring in supplies of medicine, food and ammunition."
These war horses were, of course, well looked after. New Zealand gunner Bert Stokes would later say: "To lose a horse was worse than losing a man because ... men were replaceable, while horses weren't at that stage."
There were more than 27,000 men serving in the Army Veterinary Corps and 19,000 in the Remount Department of the British Army preparing horses to be sent to war. Women, too, took their place in the receiving departments.
"First of all the horses had to be checked for all sorts of diseases and then broken so they could do the ordinary riding and pulling jobs," says Scott. "You'd prepare them so they were ready to do their jobs."
The contribution of the war horses has not been forgotten, says Scott, thanks largely, he says, to Michael Morpurgo's book "War Horse" and the film and musical inspired by Morpurgo's story about Joey, a young farm horse which is sold to the British army.
"Nothing gets anywhere near the contribution of people," says Scott. "You needed manpower but, overwhelmingly, you needed horsepower."