Allied soldiers go ‘over the top’ of their trenches to attack German lines in the battle of Somme – a four month clash in nothern France that was one of the deadliest of the war.
Members of the French association 'Memories Hairy,' dressed in World War I military outfits, carry out a historical reenactment of trench warfare in Althen des Paluds, in southern France, on Apr. 12, 2014. This year marks the 100th anniversary of the start of World War I. Jean-Paul Pelissier/Reuters
Two British officers ride camels during World War I in Egypt, with the Sphinx and a pyramid looming in the background. National World War I Museum, Kansas City, MO.
German machine gunners retreat in the battle of Belleau Wood, a fierce clash between US forces and German troops in France in 1918, during which Allied soldiers repelled a final advance by Germany on Paris. National World War I Museum, Kansas City, MO.
An explosion erupts behind thickets of barbed wire on a battlefield in Beaumont-Hamel, France. National World War I Museum, Kansas City, MO.
A group of soldiers, believed to be Austrian or Hungarian, sit in a hole caused by a grenade blast in WWI. National World War I Museum, Kansas City, MO.
Members of a German World War I historical association prepare for a walk near Verdun, in eastern France, on March 29, 2014. French and German historical association members gather annually at the battlefield, which was the site of one of the bloodiest clashes of WWI, with hundreds of thousands of lives lost. Charles Platiau/Reuters
Turkish Army soldiers march through the streets of Constantinople as the country prepares to fight Allied forces during World War I. AP/File
A French tank rolls through northeastern France. Tanks made their debut in World War I. AP/File
Soldiers from New Zealand stand next to Turkish troops during a ceremony in Gallipoli, Turkey, on Apr. 24, 2014. The annual Anzac Day event commemorates the nine-month battle between Australian and New Zealand troops, under British command, and Turkish forces on the Gallipoli peninsula in 1915. Emrah Gurel/AP
French soldiers wear gas masks in the trenches (top). World War I saw the first use of modern chemical weapons – mainly chlorine and mustard gas. National World War I Museum, Kansas City, MO.
People celebrate Armistice Day – the official end of World War I on the Western Front – in Paris on Nov. 11, 1918. The armistice famously took effect at the 11th hour of the 11th day of the 11th month. AP/File
German soldiers stand around a crashed aircraft (Fokker fighter plane) with the Iron Cross of the German Empire on the wing in eastern Germany. World War I marked the first time aircraft were used on a large scale in warfare. Sammlung Kotterba/Picture-Alliance/DPA/AP/File
American soldiers escort supply wagons pulled by mules – a reminder that, even though World War I was the first mechanized war, it retained a foot in the past. National World War I Museum, Kansas City, MO.
A firing squad executes a German spy caught near Termonde, Belgium, in World War I. AP/File
Prussian soldiers leaving Berlin for the front are given flowers by girls and women during World War I. AP/File
A memorial celebrating the Black Watch, a Scottish infantry regiment, is unveiled in Zonnebeke, Belgium, on May 3, 2014. The statue commemorates the 8,000 dead and more than 20,000 wounded Black Watch soldiers who fought in World War I. Virginia Mayo/AP