On July 11, 1952, a large attack known as Pressure Pump was conducted on the city involving 1,254 sorties from Fifth Air Force, Marine, Navy, Korean, Australian, South African, and British aircraft flying in the day, and 54 B-29s flying at night. The attack was preceded by flyers warning civilians to leave the city. On August 29, operation All United Nations Air Effort bombed the city again with 1,400 sorties.[8]