During mission briefings the target of the day was named along with a secondary or two should weather conditions prevent bombing the primary. As last resort they named one or two "targets of opportunity" the crew could choose. When returning from a mission I was looking down at a beautiful little German cross road community. A church with steeple was striking on this beautiful sunny day. All of a sudden there was an explosion and the church area was demolished. I took a look and saw a squadron of B-17s over the little town. They had picked this as their "Target of Opportunity" There was nothing there of military worth. I can still see that church steeple coming up in the air.This really upset me So I reported the incident after landing.