Of all 20th-century presidents, four led soldiers in close-combat situations.</p><p>They were Theodore Roosevelt, John F. Kennedy, George H.W. Bush and Harry Truman.</p><p>For the millions of Americans in uniform during World War II, Truman&rsquo;s service under fire became a matter of national significance as of April 1945. That&rsquo;s when Truman, the new president after the death of Franklin Roosevelt, was charged with making the century&rsquo;s most profound military decision.</p><p>Ultimately, Truman authorized the use of atomic weapons, and World War II soon ended without a traditional invasion of Japan&rsquo;s home islands.</p><p>Did Truman&rsquo;s combat experience play a role? D.M. Giangreco, a Kansas City area author who for 20 years served as an editor at Military Review, which is published at the U.S. Army Command and General Staff College at Fort Leavenworth, thinks it could have.</p><p>Giangreco has written two new books about Truman: &ldquo;The Soldier from Independence: A Military Biography of Harry Truman&rdquo; and &ldquo;Hell to Pay: Operation Downfall and the Invasion of Japan, 1945-1947.&rdquo;</p><p>Most biographers agree that Truman&rsquo;s time in uniform in World War I was perhaps the defining experience of his life. Before the war, he was a Grandview farmer.</p><p>After the war, he was a combat veteran with a new taste for leadership.</p><p>Giangreco is especially puzzled how some historians have shrugged off Truman&rsquo;s wartime service, especially the several months he spent leading an artillery battery across France.</p><p>In &ldquo;The Soldier from Independence,&rdquo; Giangreco writes that Truman&rsquo;s combat experiences &ldquo;were far more interesting and complex than previously realized.&rdquo; Also, he adds, the man who later pondered an invasion of Japan in the face of massive casualty estimates &ldquo;understood exactly what he was asking of our soldiers, sailors and marines, and he understood it at level that most Americans today would find unfathomable.&rdquo;</p><p>Giangreco maintains that the decision Truman made was an informed one and perhaps filtered through his own combat experience.</p><p>Giangreco is especially interested, for example, in how Truman once ignored orders from a colonel who directed that the exhausted men of Truman&rsquo;s artillery battery double-time up a hill.</p><p>Truman, instead, ordered the battery off the road and into the woods for a rest.</p><p>Just how Truman finessed this isn&rsquo;t entirely clear even today, although Giangreco cites evidence suggesting the colonel dressed Truman down in earnest. (&ldquo;The Colonel insults me shamefully,&rdquo; Truman wrote in a wartime journal.)</p><p>Lesson: As an Army officer, Truman was khaki to the core, but he still recognized common sense when he saw it.</p><p>If such experiences influenced Truman&rsquo;s decision in 1945, however, Giangreco suggests that they may have been trumped by the terrible casualty estimates then being given him.</p><p>Ever since a national controversy caused the 1995 cancellation of an exhibit of the Enola Gay (the aircraft used to deploy the atomic bomb over Hiroshima) at the National Air and Space Museum in Washington, the wisdom of Truman&rsquo;s decision has become the focus of what one historian, Geoffrey C. Ward, once called a &ldquo;vast quarrelsome literature.&rdquo; </p><p>Some historians think Truman made a reasonable decision in authorizing the use of atomic weapons; others maintain that he had options.</p><p>In &ldquo;Hell to Pay,&rdquo; Giangreco challenges some historians who have suggested that Japan was preparing to surrender and that casualty estimates for the planned invasion of Japan later were exaggerated.