Hechler held a series of minor appointed positions in the federal civil service until he was drafted into the United States Army during World War II in July, 1942. After graduation from Armored Force Officer Candidate School, he was assigned as a combat historian in the European Theater of Operations. Hechler helped chronicle the liberation of France, the 1944 Normandy invasion, Battle of the Bulge, and entrance into Nazi Germany. He was attached to the 9th Armored Division when an armored and infantry task force, part of Combat Command B, unexpectedly captured the Ludendorff Bridge spanning the Rhine river during the Battle of Remagen. He interviewed both U.S. and German soldiers involved at the time. He was awarded a Bronze Star and 5 battle stars. He returned after the war twice to interview Germans who took part in the battle. He found Captain Willi Bratge, one of two officers who had not been executed at Hitler's orders because he had been captured, and spent a week with him in the Remagen area learning about details of the battle. In 1957 he published the book "The Bridge at Remagen: The Amazing Story of March 7, 1945" which was adapted into a film in 1969.