With 1987's brilliant The Joshua Tree and the ensuing Rattle And Hum tour and album, this four-piece from Dublin that formed in high school in 1976 earned the unwieldy mantle of "The Biggest Rock and Roll Band In The World". How does one artistically answer or live up to that title? This challenge is the true test of a band's mettle, and U2 proved it could handle anything with 1991's stunning Achtung Baby.

Achtung Baby is nothing less than a rebirth. In the powerful aura of a reunited Berlin, U2 repaired to the studio with a masterful production team and strode boldly into the information age. On one hand, the band had almost nothing to prove, having already cemented its place in rock history. But, on the other hand, U2 had everything to prove, largely because Rattle And Hum was such a mixed effort, and not the kind of artistic leap for which the group had become known.

In the three years afterward, music and pop culture struggled to move away from all things '80s. But when Achtung was dropped, all was clear: U2 understood what was going on, and they were able to captivate with a rock album of a different breed. As Bono proclaimed in opener "Zoo Station," they were ready for the laughing gas.

Where once were chiming, clean guitars and imagery of the sun rising over Utah hills, now were metallic, shimmering walls of sound, bold rhythms and nighttime in the modern city.

The guttural riff that introduces the record and the siren wail of "Even Better Than The Real Thing" display The Edge's innovative guitar playing at a new level. He still loves the echo loops, but the tones he stretches out on Achtung are much more diverse and cinematic than on the few previous U2 records. His riffing on "Until The End Of The World" and "Mysterious Ways" prefaced the rhythmic intensity of '90s axe whiz Tom Morello of Rage Against The Machine.

As rhythmically astute as they were on previous U2 albums, bassist Adam Clayton and drummer Larry Mullen Jr. infuse Achtung Baby with a more pronounced beat. The attention to bottom end manifests itself in dance rhythms, bass and keyboard loops, and synthetic percussion. While the band's infatuation with machine music was taken almost too far on 1997's Pop, Achtung strikes a perfect medium, seamlessly blending the organic with the electronic.

And it wasn't all murky. Rising out of such dark surroundings, "One" might be the love song of the '90s. That simple, lilting minor-key melody found the lovesick dreamer in all of us, wallowing in bleak self-deprecation ("You gave me nothing, now it's all I got") but yearning for the promised land of love ("One life, with each other / sister, brother").

Where "The Fly" is a spooky electro-glam-goth rave-up, "So Cruel" is a tension-building exercise with a phat backbeat. "Who's Gonna Ride Your Wild Horses" rides in on caressing waves of phased guitar and disorted keyboard tones, more My Bloody Valentine than Bowie.

The all-star production crew of Brian Eno, Daniel Lanois, Steve Lillywhite and Flood helps all these sonic experiments find form. The song structures for the most part stay rooted in U2's anthemic rock realm, but Achtung's instrumentation and sounds brought a completely new palate to rock's table, inspiring such '90s mainstays as Radiohead and R.E.M.

On Achtung Baby, U2 reminds us why we fight. The album slinks through desolate cityscapes but pauses to look up at the stars and ponder immortality. It reminds us that there is still beauty in the concrete night.