Book excerpt: Dispatched on what was to be an easy assignment of attacking the Privoser Oil Refinery and associated railroad yards at Moravska Ostrava, Czechoslovakia, the 20th Squadron of the 2nd Bombardment Group saw the bloodiest day in their history. Not a single one of the 20th Squadron's B-17 bombers returned from the mission. In this book, the 90 airmen on that mission provide a remarkable personal window into the Allies' Combined Bomber Offensive at its height during World War II. Their stories encapsulate how the U.S. Army Air Force built, trained, and employed one of the mightiest war machines ever seen. These stories also illustrate, however, the terrible cost in lives demanded by that same machine.