On August 29, 1944, the 15th U.S. Army Air Force unleashed a 500-plane raid against oil and rail targets throughout central Europe. The mission's planners directed the 20th Squadron of the 2nd Bombardment Group to do what they regarded as an easy assignment: attack the Privoser Oil Refinery and associated railroad yards at Moravska Ostrava, Czechoslovakia. This 'milk run' deteriorated into the bloodiest day in the 2nd Bombardment Group's history: Not a single B-17 Flying Fortress bomber returned from the mission. Forty airmen were killed, another 46 spent the rest of the war as POWs, and only four, with the aid of the OSS and anti-German partisans, managed to evade capture and escape to Allied lines. The ninety airmen on the mission to Moravska Ostrava provide a remarkable personal window into the Allies' Combined Bomber Offensive at its height during WWII. In a microcosm, their stories encapsulate how the U.S. Army Air Force built, trained, and employed one of the mightiest war machines ever seen. Their stories also illustrate, however, the terrible cost in lives demanded by that same machine.