Jethro Tull already had made three albums when Aqualung was released on March 19, 1971. But none of those records had the force, songs or lasting influence that their breakthrough LP almost immediately drilled into the public consciousness. And they did it with a smart, and often questioning, album that went way beyond the usual rocks-off stuff of the era.

That's probably to be expected from a band whose leader, Ian Anderson, was a flute-wielding deep-thinker who looked like an anxiety-stricken college professor and had the tendency to stand on one propped leg during his most intense bouts of soloing.

To get to this point, the group needed to make some changes first. They got a new keyboardist and a new bass player, but more importantly, they turned down the heavier electric elements of previous albums like Benefit and Stand Up and replaced them with more pastoral, acoustic sounds. And, fitting for a band whose frontman resembled a 17th-century troubadour, the change fit them perfectly.

Working a little bit of prog, some straightforward rock 'n' roll and whole lotta folk into their new songs, Jethro Tull recorded the bulk of Aqualung during three months of sessions in London over the winter of 1970-71.

Even though they were primarily unplugged now, the songs actually sounded harder thanks to Anderson and the band's new focus on riffs. The opening title track is the most obvious example, but other prime album cuts -- particularly "Cross-Eyed Mary," "Hymn 43" and "Locomotive Breath" -- rank among Tull's all-time best. At times, the record plays like a greatest-hits collection.

Added to all this was a central theme of faith and its place in society through the ages. Side one is told through a more secular position, while the second half (subtitled "My God") explores religion and its mostly negative effect on the masses. Aqualung isn't exactly a concept album, but it plays a lot closer to one than many records that claim to be. And it makes a whole lot more sense.

Listen to Jethro Tull's 'Aqualung'

Thematic ties aside, the album holds together because of the more direct and focused musicianship. Somewhere between 1970's Benefit and Aqualung, Anderson found new songwriting inspiration (reportedly, British folkies Roy Harper and Bert Jansch helped shape this new direction) and more freedom to explore his natural musical and intellectual tendencies.

The album's success -- it was the first Tull album to crack the Top 10 and led to two straight No. 1s, 1972's Thick as a Brick and the following year's A Passion Play -- set the group on a new, fruitful path. They never made a better album, or a bigger-selling one, but it inspired, both directly and indirectly, records like Thick as a Brick (Anderson's blatant concept-album reaction to Aqualung's supposedly nonexistent concept) and 1975's Minstrel in the Gallery. And it made them huge. Bigger stages for all those flute solos were looming on the horizon.

See Jethro Tull Among Rock’s Most Underrated Albums

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