WW2 warning sirens

A network of sirens was installed during WW2 to give the population warning of approaching bombing raids and maybe to warn of other impending disasters.  They looked a little like lamppost without a lamp. They were tested regularly and I remember hearing them in the 50s - maybe the 60s too. The noise was unmistakable - a howl starting low and rising higher before going down again, an awful sound which used to get me in the gut. During the cold war, they were also supposed to give the 4 minute warning of an approaching nuclear attack from the Communist East. Never understood how one would protect oneself against a nuclear attack in 4 minutes . . . .