Although it wouldn’t appear on American record store shelves until the early months of 1971, Black Sabbath’s seminal sophomore album Paranoid began invading the U.K. (and Europe) on Sept. 18, 1970. It quickly raced up the charts in many countries and reached an astonishing No. 1 in their homeland.

In doing so, Paranoid proved that the wholly unexpected Top 10 success enjoyed by the Birmingham quartet’s modestly recorded self-titled debut, released barely six months prior, had been anything but a fluke. Still, for vocalist Ozzy Osbourne, guitarist Tony Iommi, bassist Geezer Butler and drummer Bill Ward, Paranoid was just a hastily assembled collection of the best songs they had to offer – even as they were learning to cope with a hurricane of fame, well beyond their wildest expectations.

But at least the four young men knew better than to mess with their winning formula. They once again retained producer Roger Bain and, other than enjoying the luxury of spending more time in the studio (versus the frantic 24 hours afforded to their debut), also maintained their songwriting penchant for wanton, unrefined musical power. Their lyrics avoided pop music’s traditionally pithy stories of love and lust in favor of more desperate subjects steeped both in the occult and real-life terrors.

To wit, Paranoid’s opening epic “War Pigs” started out named “Walpurgis,” before lyricist Butler swapped satanic ritual for equally evil warmongering. The future doom standard “Iron Man” shrouded apocalyptic allegory under the guise of dark fantasy, while “Electric Funeral” cut right to the chase. The terrifying “Hand of Doom” contained graphic warnings about heroin addiction.

Even a song as surreal-seeming as “Fairies Wear Boots” was actually inspired by run-ins with belligerent skinheads at Black Sabbath’s shows. And though Paranoid’s sonic wildcard, “Planet Caravan,” professed science fiction musings over its unnaturally gentle, psychedelic dreamscape, the provocatively named “Rat Salad” was clearly just a platform for Ward to shine, based on John Bonham’s “Moby Dick.”

Finally, there was the bite-sized, frantic title track, which was jammed together so quickly in a fit of spontaneous inspirational combustion, that reading too much into its hastily coupled words is both unwise and, frankly, unnecessary — except to point out how its vague ramblings on loneliness, misery, and general confusion about one’s lot in life once again connected with disenfranchised listeners everywhere.

Needless to say, it was precisely this vast population of marginalized youths, feeling excluded by society, that started flocking into Black Sabbath’s growing fan base around the world, lured by Paranoid’s undeniable destiny to become heavy metal’s definitive watershed.

Nothing has changed since Paranoid's release. Heavy metal continues to seduce generation after generation of rebellious kids seeking music they can relate to, and vent their pent-up frustrations and aggression to — all of it facilitated by the thousands of subsequent albums that can trace this fundamental purpose and usefulness to Black Sabbath and their most important career’s achievement, Paranoid.

Black Sabbath Albums, Ranked Worst to Best