 Complete the following phrase:  After the US entered into the war, the US opposed such a bombing, fearful of offending Catholic members of its military forces, but said that they could not stop the British from bombing Rome if the British so decided. The US military even exempted Catholic pilots and crew from air raids on Rome and other Church holdings, unless voluntarily agreed upon. Notably, with the exception of Rome, and presumably the possibility of the Vatican, no Catholic US pilot or air crew refused a mission within German-held Italy. The British uncompromisingly said they would bomb Rome whenever the needs of the war demanded. In December 1942, the UKs envoy suggested to the Holy See that Rome be declared an open city, a suggestion that the Holy See took more seriously than was probably meant by the UK, who did not want Rome to be an open city, but Mussolini rejected the suggestion when the Holy See put it to him. In connection with the Allied invasion of Sicily, 500 US aircraft 