This essay is based on the author's presentation at the Wachman Center's July 26-27, 2008 History Institute for Teachers, co-sponsored and hosted by the Cantigny First Division Foundation of the McCormick Tribune Foundation. In an effort to better comprehend what he designates "the greatest calamity in human history," the author presents ten points every American student ought to know about the U.S. Army in the Second World War: (1) The U.S. Army was a puny weakling when the war began; (2) The war encumbered all of America; (3) The U.S. Army did not win World War II by itself; (4) The U.S. Army's role in the liberation of Europe did not start at Normandy; (5) The U.S. Army for some considerable time after we entered the war was not very good; (6) The U.S. Army in WWII comprised much more than just riflemen; (7 ) The Army remained under civilian control throughout the war; (8) The U.S. Army in WWII was among the greatest agents, perhaps the greatest agent, of social change in the country during the 20th century; (9) The history of the U.S. Army in WWII is among the greatest stories of the 20th century; and (10) They died for you.