By the guidelines set down by the Selective Service Act, all males aged 21 to 30 were required to register to potentially be selected for military service. At the request of the War Department, Congress amended the law in August 1918 to expand the age range to include all men 18 to 45, and to bar further volunteering.^[7] By the end of World War I, some two million men volunteered for various branches of the armed services, and some 2.8 million had been drafted.^[8] This meant that more than half of the almost 4.8 million Americans who served in the armed forces were drafted. Due to the effort to incite a patriotic attitude, the World War I draft had a high success rate, with fewer than 350,000 men “dodging” the draft.

– Selective Service Act of 1917, Wikipedia