The U.S.-led coalition against the Islamic State sends off two bombing sorties every hour, and has for more than 450 days. That can be hard to visualize, so BBC News added an audio component in this fascinating look at how the anti-ISIS bombing campaign compares with previous wars. If two bombing raids an hour "sounds relentless," says the BBC's Neal Razzell, "listen to what Serbia faced during the 1999 NATO bombing campaign," or Iraq faced in the 2003 U.S.