The right answer is increase the size of the armed forces by using the draft.
In the heat of the WWI and the decision to enter the war, the USA had only a combined strength of the regular army and National Guard of only 379,000 combatants. The need for a large number of troops forced Wilson to implement a military draft called Selective Service Act of 1917, where all men aged twenty-one to thirty (later, eighteen to forty-five) could be drafted for military service. About 2 million mostly under-trained American troops crossed the Atlantic, and about 1.4 million saw at least some combat, including 42,000 African Americans. In the end, all the USA combined strength total of 3.7 million.