An air raid is an attack by military aircraft on ground-based targets.
I believe that most major cities in countries that had been involved in World War II had air raid sirens. The idea was that if the siren were turned on you’d head for the nearest bomb shelter, which might have simply been a solid basement or a subway tunnel.
I wonder if those air raid sirens still exist and work. Probably not. If they did, it’s inevitable that some idiot with access to them would get the bright idea to set them off to celebrate the local team’s win in a national, regional or international sporting tournament.
I’ve never heard air raid sirens go off here in Toronto, so I guess they don’t exist. Then again, like I said, I live in Toronto. Our teams almost never win championships, so who knows?