As late as 1917, the United States maintained only a small army, one which was in fact smaller than those of thirteen of the states already active in the war. After the passage of the Selective Service Act in 1917, it drafted 4 million men into military service. By the summer of 1918, about 2 million US soldiers had arrived in France, about half of whom eventually saw front-line service; by the Armistice of November 11 approximately 10,000 fresh soldiers were arriving in France daily. In 1917, Congress gave US citizenship to Puerto Ricans when they were drafted to participate in World War I, as part of the Jones Act. In the end, Germany miscalculated the United States' influence on the outcome of the conflict, believing it would be many more months before US troops would arrive and overestimating the effectiveness of U-boats in slowing the American buildup. Beginning with the Battle of Saint-Mihiel, the first major battle involving the American Expeditionary Forces, the leaders of the United States war efforts were General of the Armies John J. Pershing, Navy Admiral William Sims, and Chief of Air Service Mason Patrick.