Operation Tidal Wave was an air attack by bombers of the United States Army Air Forces (USAAF) based in Libya on nine oil refineries around Ploiești, Romania, on 1 August 1943, during World War II. It was a strategic bombing mission and part of the "oil campaign" to deny petroleum-based fuel to the Axis powers. The mission resulted in "no curtailment of overall product output".
This operation was one of the costliest for the USAAF in the European Theater, with 53 aircraft and 500 aircrewmen lost. It was proportionally the most costly major Allied air raid of the war, and its date was later referred to as "Black Sunday". Five Medals of Honor and 56 Distinguished Service Crosses, along with numerous other awards, went to Operation Tidal Wave crew members. A 1999 research report prepared for the Air War College at Maxwell Air Force Base in Alabama concluded that the bombing campaign in Ploiești was "one of the bloodiest and most heroic missions of all time". One of the downed American planes crashed into a female prison in Ploiești, resulting in about half of the civilian casualties from the total of 101 killed and 238 injured.