Here is a graph that compared the amount of time it took for both the British Army and the American Army to have 2,000,000 soldiers on the Western Front during World War One:
"The British sent to France many more men in their first year in the war than we did in our first year. On the other hand, it took England three years to reach a strength of 2,000,000 men in France and the United States accomplished it in one half the time."
Click here to read more statistics about the American military of the First World War.