It's not just human soldiers who fought for their country.
Millions of horses and other animals also served during wartime, and one special photo shows just how much their human counterparts appreciated the war horses and their sacrifice.
The touching black and white photo is believed to have been taken by officers of the Auxiliary Remount Dept. No.326 in Camp Cody, New Mexico in 1915.
The image shows about 650 soldiers standing in a formation that, from above, resembles a cavalry horse's head, neck, and bridle — a true tribute from the soldiers to the many horses who fought, and often died, by their side in the Great War.
While horses have served in many other wars, the large number of horses killed in WWI was staggering; about eight million horses, and countless mules, and donkeys were lost in the war. The U.S. Army and the British Army both used mounted infantry while Germany stopped sending them to the Western Front early on in the war. The horses suffered terrible conditions, and were killed most often on the front lines by machine gun fire and gas attacks.
Horses and their counterparts also helped carry food, water, ammunition, gas masks and medical supplies in supply wagons over long distances and rough terrain to the allied forces on the front lines. Their bravery inspired the book "War Horse," by Michael Morpurgo, which was later adapted into a film of the same name directed by Steven Spielberg.
The movie tells the tale of Joey, a bay Thoroughbred horse who endures many of the common horrors of war after being sold into the British cavalry.
Multiple nonfiction books have been written on the topic as well, including the 2011 book "The War Horses: The Tragic Fate of a Million Horses in the First World War" by historian Simon Butler.
It was Butler who referred to WWI as "the first and last global conflict in which the horse played a vital role."
About his book, Butler said:
"I was always interested in this subject, but I never realised how what happened to the horses was not properly documented before. My whole book is about the tragic story of how these ordinary horses were taken from farms by the military ... For the men who served in the trenches it was a tragedy and for the people at home it was a tragedy too because they lost animals to which they had become attached."
But while this war memorial may not have been well documented in the history books, the photo makes it clear that, to the soldiers who served with them, the horse's war effort sacrifice never went unnoticed.
Do you find this soldier's tribute touching? Share your thoughts below.
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