 In April 1971 , Aqualung peaked at number four on the UK Album Chart ; when the CD version was released in 1996 , it reached number 52 . It peaked at No. 7 on the Billboard Music Charts ' North American pop albums chart ; the single " Hymn 43 " hit No. 91 on the Billboard Hot 100 chart . The album would go on to sell over seven million copies , and is the band 's best @-@ selling album . Aqualung was one of only two Jethro Tull albums released in quadraphonic sound , the other being War Child ( 1974 ) . The quadraphonic version of " Wind Up " , which is in a slightly higher key , is included on the later CD reissue of the album as " Wind Up ( quad version ) " . 
