By the turn of the '90s, U2 were at a crossroads. They were a major stadium act, but creatively they were faltering. The band had been stung by media criticism of their half studio / half live double album Rattle and Hum. That 'toying' with Americana certainly delivered some hits ("Angel Of Harlem," the Bo Diddley-esque "Desire," the B.B. King duet "When Love Comes To Town") but many found the album too much of a pastiche. U2 suddenly became the most loved/hated rock band on the planet. What to do? As Bono told a Dublin crowd in the late '80s: "We have to go away and dream it all up again."

As guitarist Edge later reflected, the 'traditionalism' of Rattle And Hum was the exception in the U2 canon. "My view," he told this author in 1996 "is that Rattle And Hum, for all its traditionalism, is actually our 'experimental' record. Achtung Baby got us back to our normality � making dark, very European music with experimental sounds." Famously, U2 decided to impose new rules for Achtung Baby, the band's rebirth.

Bono: "Buzzwords on this record were trashy, throwaway, dark, sexy and industrial (all good) and earnest, polite, sweet, righteous, rockist and linear (all bad)."

But the sessions, in Berlin's Hansa Studios nearly collapsed completely. U2 had booked Hansa hoping to capture the "greatness" of two of their favorite albums: David Bowie's Low and Heroes that were recorded there. But when they turned up, they couldn't even write a song. "The greatness," Bono laughs on the new U2 documentary From The Sky Down, "had left the building."

Bassist Adam Clayton admitted in Bill Flanagan's biog U2 At the End of the World, constant touring in each other's pockets had taken its toll: "We had to decide how much we liked each other� I'm not saying that was easily resolved."

But "One" rescued them. U2 were struggling to come up with anything all four felt was good enough. Bored of hammering at a demo called "Sick Puppy" (that later morphed into "Mysterious Ways"), Edge hit on an off-the-cuff chord progression that would become "One."

"At the instant we were recording it, I got a very strong sense of its power," Edge told Irish journalist Neil McCormick. "We were all playing together in the big recording room, a huge, eerie ballroom full of ghosts of the war, and everything fell into place. It was a reassuring moment, when everyone finally went: 'Oh great, this album has started.' It's the reason you're in a band - when the spirit descends upon you and you create something truly affecting. "One" is an incredibly moving piece. It hits straight into the heart."

"One" is atypical of Achtung Baby in sound, but it did kickstart U2's creativity. Some think the lyric is schmaltz: but the "one life, with each other, sisters, brothers�" line was later voted the greatest ever song line by VH1 viewers in 2006. "Earnest, polite, sweet, righteous, and linear?" "One" is all those, but if U2 hadn't dreamed that song up Achtung Baby may have collapsed into nothing.

But after "One," other songs soon formed. Maybe as a reaction to "One", U2 felt free to get more aggressive. Lyrically, Achtung Baby was a volte-face for U2. Bono, for all his '80s piety and flag waving, came to realize: "Rock 'n' roll is ridiculous," he told Rolling Stone on Achtung Baby's release." In the past we were trying to duck that. Now we're wrapping our arms around it and giving it a big kiss."