The time needed to train and organize the American Expeditionary Forces (AEF) meant that American troops did not engage in extensive combat until spring 1918. That spring, German troops had left their trenches and launched a series of major offensives trying to win the war before the Americans arrived in even greater numbers. In early June, the fight for Belleau Wood, a boulder-strewn forest close to Paris, was one of the AEF's early battles. There, the U.S. 2nd Division, a combination of Army and Marine Corps units, helped the French repel a German offensive and then retook Belleau Wood in a ferocious battle that lasted twenty days. For the Marines, who faced the heaviest fighting, June 6, the first day of their assault was the bloodiest day in the Corps' history up to that point, leaving 222 dead. Belleau Wood took on special meaning for Marines as a demonstration of the Corps' bravery and tenacity.