and ... dream it all up again". Wishing to reinvent themselves and seeking inspiration from German reunification, the group de-camped to Hansa Studios in Berlin in October 1990 with producers Daniel Lanois and Brian Eno to record Achtung Baby. The sessions were fraught with conflict, as the band argued over their musical direction and the quality of their material. Weeks of tension and slow progress nearly took their toll: the group considered breaking up, but they made a breakthrough with the improvised writing of the song "One". With improved morale, the group completed the album in Dublin in 1991. In November, Achtung Baby was released to critical acclaim. Musically, it incorporated influences from the alternative rock, electronic dance music, and industrial music of the time. Thematically, it was a more introspective and personal record; it was darker, yet at times more flippant than the band's previous work. The album and the subsequent multimedia-intensive Zoo TV Tour were central to the group's 1990s reinvention, whereby they abandoned their earnest public image for a more lighthearted and self-deprecating one. Achtung Baby has been one of the group's most commercially successful records, selling 18 million copies. Production To commemorate the 20th anniversary of Achtung Babys original release, U2 reissued the record in several formats in October 2011. Leading up to the anniversary, the band was unsure how much attention to pay to a past album while still actively writing and recording new material. Guitarist The Edge said, "How big a deal do we make of an anniversary when we're in the middle of what we're doing now? We had a hard time figuring that out. We're not a heritage act. We're still very active. But this record was so pivotal that we felt it was OK to revisit it." Director Davis Guggenheim was subsequently commissioned by the band to make a film about Achtung Baby in six months. As a fan of U2 since his youth and having previously collaborated with The Edge for the 2008 documentary It Might Get Loud, Guggenheim agreed to the project. His goal for the film was to explain how U2 managed to remain together for so long, in contrast to other rock groups that have been undone by internal conflict; he described the band's longevity as "fighting against that law of physics". Guggenheim also sought to tell the story of how the band transformed themselves musically over