During World War II, Braunschweig (known as Brunswick in English) was attacked by Allied aircraft in 42 bombing raids. On the night of 14/15 October 1944, the attack by No. 5 Group Royal Air Force (RAF) marked the high point of the destruction of Henry the Lion's city during the war. The air raid was part of Operation Hurricane, which was designed to demonstrate the capabilities of the Allied bombing campaign. The attack caused a massive conflagration, that might have developed into a firestorm, and resulted in Braunschweig burning continuously for two and a half days from 15 to 17 October. More than 90 percent of the medieval city centre was destroyed, changing the city's appearance to the present day.