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W. Britain
The first American troops landed in Europe in June 1917. However, the inexperienced soldiers of the American Expeditionary Force required extensive training for modern trench warfare and were not able to participate at the front until late October 1917. By the summer of 1918 approximately a million US Soldiers had arrived in France, about half of whom eventually saw front-line service.
By the time the Armistice has suspended all combat operations, the AEF had evolved into a modern, combat-tested army.