The Selective Service Act was drafted by Brigadier General Hugh Johnson after the United States entered the First World War. The law authorized President Woodrow Wilson to raise a volunteer infantry force of not more than four divisions.
All males between the ages of 21 and 30 were required to register for military service. By 12th September 1918, 23,908,566 men had registered. Around 4,000,000 men were ultimately drafted into the armed services. Of these, 50 per cent served overseas during the war.