Black Sabbath's second album Paranoid would prove to be not only one of the most defining moments of their catalog, but also for heavy metal.

With their self-titled debut album, Black Sabbath had established a style all its own and had started to build a devoted audience. Paranoid followed a similar path, but with a more focused energy and greater detail to songwriting, both of which helped open the door to worldwide commercial success.

The album kicks off "War Pigs," which was the original working title of the LP before its Jan. 7, 1971 release in the U.S., four months after its Sept. 18, 1970 arrival overseas. The doom-laden, riff-heavy track is a powerhouse, not only musically but lyrically as well, ranking as one of the era's most potent anti-war songs.

Listen to Black Sabbath's 'War Pigs'

"You could just see a lot of things going wrong in the world, and nobody was saying anything about it," bassist and lyricist Geezer Butler recalled in the documentary Paranoid: Classic Albums. "Bob Dylan had long since faded from the present memory and there was nobody talking about the stuff I wanted to talk about, political stuff, so that's what inspired me."

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The band is noticeably tighter and the songs are more focused throughout. The title track is a solid rock 'n' roll punch, distilling the Sabbath sound into a straight-ahead three-minute cut. At its core, the basic riff contains punk-rock energy with a razor-sharp metallic attack. Ozzy Osbourne's vocal is spot-on, and Rodger Bain's production still resonates with brutal power all these years later.

Black Sabbath's 'Paranoid' Had a Beatles Influence

Gears shift on "Planet Caravan," a moody, psychedelic number that rolls along waves of conga drums, phased vocals and mellow guitars. It's another example of Black Sabbath's versatility. "We always liked variation," said Butler. "I think that's another Beatles influence. We didn't do a 'heavy metal' album from track one to track 10."

The classic "Iron Man" rounds out side one, with Tony Iommi's guitar riff taking its place among of rock's all-time greatest. The tale of overcoming obstacles and seeking revenge in a world gone wrong connected perfectly with the band's fans and, along with the title track, helped get Black Sabbath on U.S. radio for the first time.

Listen to Black Sabbath's 'Iron Man'

Side two kicks in with the evil glowing stomp of "Electric Funeral," which continues the themes of despair and impending apocalypse. Osbourne's vocal follows Iommi's guitar and Butler's bass to create a powerhouse wall of sound. The song breaks off midway for a metallic jazz spiral, before landing firmly back on planet riff.

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"Hand of Doom," with a jagged riff at its heart, tackles drug addiction – particularly, the horror of soldiers returning from Vietnam as junkies. "Rat Salad" serves as a brief showcase for drummer Bill Ward and sets the table for album closer "Fairies Wear Boots," whose jazz-driven tempo takes the song into another yet another direction. Iommi, Ward and Butler create a sonic metal swing groove that gets heavier and heavier as it sails along.

Paranoid just missed the Top 10 in the U.S., paving the way for the band's continued accession. (The album topped the U.K. charts a a few months earlier.) "It was such a brilliant time," Ward recalled in an interview with Kerrang. "We were constantly touring. The music was the beginning of a new era. I think it was the crucible of something that was to be way bigger than us."

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Gallery Credit: Eduardo Rivadavia

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