The United States' entry into World War I In April 1917 exposed an American military weakness. Not only did the U.S. have a small army but even after a recruitment drive was expected to swell its ranks, it was obvious that the merchant fleet was not big enough to ferry the nascent American Expeditionary Force across the Atlantic and, once it was there, keep it supplied and fed. Ten days after the United States entered World War I, the United...