The papacy was one of the most vocal opponents of aerial bombardment. This was a consistent policy that began well before the Allies started to bomb Germany. The Vatican issued denouncements of such practices in WWI and updated their opposition when Guernica was bombed in 1937 during the Spanish Civil War. Throughout WWII Pius XII (the pontiff throughout the conflict) consistently called upon all parties in the war to cease the practice of targeting noncombatants--especially via indiscriminate aerial bombardment. For instance, in section 106 of Summi Pontificatus

Venerable Brethren, the hour when this Our first Encyclical reaches you is in many respects a real "Hour of Darkness" (cf. Saint Luke xxii. 53), in which the spirit of violence and of discord brings indescribable suffering on mankind. Do We need to give assurance that Our paternal heart is close to all Our children in compassionate love, and especially to the afflicted, the oppressed, the persecuted? The nations swept into the tragic whirlpool of war are perhaps as yet only at the "beginnings of sorrows" (Saint Matthew xxiv. 8), but even now there reigns in thousands of families death and desolation, lamentation and misery. The blood of countless human beings, even noncombatants, raises a piteous dirge over a nation such as Our dear Poland, which, for its fidelity to the Church, for its services in the defense of Christian civilization, written in indelible characters in the annals of history, has a right to the generous and brotherly sympathy of the whole world, while it awaits, relying on the powerful intercession of Mary, Help of Christians, the hour of a resurrection in harmony with the principles of justice and true peace.

Later in the war the pontiff would call upon FDR to forswear bombing cities in Italy. When that initiative was rebuffed there was an attempt to have the Allies cease their bombing of Rome specifically. This attempt was similarly unsuccessful. In fact, the Vatican was criticized by both the Axis and the Allies for its opposition to aerial bombardment. Both sides asserted that the Vatican was favoring the other side and was taking sides in the conflict.