A little after midnight on June 16th, 1997, two Irishmen walked into the US immigration pre-clearance facility at Edmonton International Airport in Canada. One wore a silk boxer’s dressing gown with the hood up, his eyes concealed behind mirror shades. The second sported a goatee and was dressed head-to-toe in a white cowboy outfit studded with rhinestone and topped with a vast stetson hat. Under the fluorescent lights of the near-deserted terminal, he looked like a neon ornament brought to life.

Bono and The Edge had come straight from the stage at the city’s Commonwealth Stadium and were hastening towards a flight to San Francisco. Behind the sunglasses Bono could barely keep his eyes open as he filled in the immigration form. The two Edmonton gigs had gone well – certainly better than an instantly notorious concert two months earlier at which U2 had stopped midway through a new song in order to work out to play it.

But he was nonetheless exhausted – physically and emotionally too. Seven weeks into their most ambitious – and expensive – tour to date, the frontman dressed as a boxer was feeling punch-drunk from defending U2’s title as the biggest band in the world.

Twenty-one years on, it seems ludicrous that U2’s position as one of rock’s heavyweights could ever have been under threat. They roll into Dublin’s 3Arena on November 5th for four nights, part of a blockbusting global trek which has to date grossed $106 million.

How different it all was in 1997 as, in service of opinion-splitting new album Pop, they struggled against some of the most sustained setbacks of their career. True, in places such as Edmonton – provincial, happy to be on the international touring circuit – the greeting afforded the PopMart tour had been as full-hearted as U2 had come to expect.

Was this a parody of consumerism? A sneer at it? A commentary on U2’s own descent into irony? Were U2 making a joke – or was the joke on them? Yet elsewhere their public appeared not quite to understand U2’s latest concept: a run of dates that doubled as playful commentary on consumerism and the disposability of modern art. The bafflement had filtered through to underwhelming box office. On May 16th, a concert at the 80,000-capacity Clemson University Memorial Stadium in South Carolina had drawn only 22,000. At Denver’s Mile High stadium, some 30,000 had turned up for U2 – less than half the capacity.

Heart, soul and chequebook The stakes had never been higher for the group, who had committed heart, soul and chequebook to PopMart. With operating costs of $214,000 a day, the set featured the world’s largest LED screen, an (instantly infamous) animatronic lemon, an olive on a 100ft toothpick and a huge fibreglass arch – a wink towards the McDonald’s church of conspicuous consumption – at the top of which nestled 60 orange speakers.

The problem was that the zany presentation was in service of a muddled message. Was this a parody of consumerism? A sneer at it? A commentary on U2’s own descent into irony on their previous tour, the boundary-busting Zoo TV? In other words, were U2 making a joke – or was the joke on them?

“A big reason the Pop era has been largely written out of U2’s history is because at the time it was seen as a mis-step for the band,” says Alan Cross, author of U2: The Secret History. “By the band’s later admission, the album was rushed and unfinished, crippled by release schedules and the need to launch a tour. I don’t think people got the joke and pokes at consumerism. And perhaps going on tour with an occasionally non-functioning giant lemon sent the wrong message.”

Every successful band goes through that period where it seems they’ve forgotten why they picked up their guitars in the first place. But few have arguably committed as many strategic errors and presented their critics with such an easy target as U2 did around Pop. The cardinal sin, as Cross suggests, was to announce a world tour with their ninth album as yet uncompleted.

Bono on stage during the PopMart tour. Photograph: Terry Thorp Eager to build on what had been accomplished with Zoo TV, the band’s manager, Paul McGuinness, pushed U2 to exclusively tour stadiums for their next run of dates (Zoo TV had started with smaller indoor venues). By every account, the group weren’t entirely convinced about the strategy – and were meanwhile trying to knuckle down on their problematic new LP. However, the wheels inevitably trundled forward and the dates were booked. Come what may, U2 would be hitting the road in April 1997. Related ‘Trust yourself. Be a good friend’: Bono’s ‘six thoughts for sixth class’

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Pop still hadn’t been finished as U2 shuffled before a scrum of reporters at a KMart in Greenwich Village, New York on February 12th to announce the new tour.

Discount supermarket The first question – aside from when the new album would be ready – was why U2 were giving a press conference in a discount supermarket. Bono, usually so smooth before the flashbulbs, didn’t have a straightforward answer. Indeed, he appeared as baffled as anyone else why U2 were about to devote 11 months to a tour inspired by US retailing.

“I can’t quite recall how it got to the idea of taking a supermarket on the road,” he shrugged. “I remember it making a lot of sense at the time. As I’m sitting here I’m trying to think what that [reason] is.”

The Edge couldn’t see his guitar pedals during the encore rendition of Discotheque, the widely-disliked lead single from Pop Just how unprepared U2 were became obvious on the opening night in Las Vegas on April 25th, six weeks after the dance-flavoured Pop had been released to mediocre reviews (it would drop out of the US charts after just three weeks).

The pressure had been immense, with more than 350 journalists gathered at the 37,000-capacity Sam Boyd stadium and the VIP area heaving with stars such as Christian Slater, Winona Ryder, Sigourney Weaver and REM. But while the opening to the concert had been as bombastic as fans would have expected, with the group walking through the crowd to the strains of M’s Pop Musik, behind the scenes things had not gone smoothy.

Screen grab from PopMart TV: Bono appeared as baffled as anyone else why U2 were about to devote 11 months to a tour inspired by US retailing Twenty-four hours earlier, U2 had summoned their crew to their dressing room for a stern talking-to after the hydraulic lemon – which was to carry the band through the air and disgorge them for the encore – had become stuck in mid-air.

But now, with half the world watching, it was U2 themselves who were mucking up. A performance of their new single Staring At The Sun – which Bono felt had the potential to be an anthem to rival Achtung Baby’s One – broke down a minute in, with each of the four musicians seemingly playing in a different tempo.

“Talk amongst yourselves,” Bono told the crowd. “We’re just having a little family row.” They started again and just about got through the track, which would quickly be retooled as an acoustic piece performed by The Edge and Bono alone.

Too much dry-ice Incredibly, worse was to come that evening. The lemon functioned as planned but, suffering opening night nerves, the crew flooded the stage with too much dry-ice. Consequently, The Edge couldn’t see his guitar pedals during the encore rendition of Discotheque, the widely-disliked (in the US at any rate) lead single from Pop.

“He needed to step on a switch on his foot-pedal which was . . . somewhere down there on the floor,” recalled U2 show director Willie Williams in his online diaries. “Later he told us that he was completely blind in the fog, so sank to his hands and knees to try to find it by touch. Finding himself at the world premiere of his new show, on his knees feeling about the floor, he started to laugh. A little voice came into his head: ‘It has finally happened . . . I am Derek Smalls – this is Spinal Tap.’”

The Edge arrives onstage at Lansdowne Road during U2’s PopMart tour in August 1997. Photograph: Terry Thorp Even by the standards of U2 in the 1990s, PopMart was a daunting undertaking. Overheads each day were $90,000 higher than Zoo TV. This translated to higher ticket prices, averaging at a nosebleed $50 in the US. And, unlike other mega-bands such as The Rolling Stones, U2 were working without a corporate sponsor – something they would amend by 2009’s Blackberry-backed 360 Tour. Instead they had turned to Canadian promoter Michel Cohl to underwrite PopMart.

Cohl, by all accounts, expected full-house signs everywhere. He anticipated PopMart grossing $260 million – $20 million more than the Rolling Stones’ Steel Wheels tour, which he had also backed. But when Pop was finally released (the band would later describe the scrappy collection as the world’s most expensive demo), its swerve into electronica was perceived as a mis-step, especially in the US. In the event, PopMart would bring in a “mere” $171 million.

The fact the band were rushing to make the April kick-off for the tour didn’t help either. “The music wasn’t where they wanted it to be and the ambitious, oversized shows offered a host of technical difficulties,” wrote Kim Washburn in Breaking Through by Grace: The Bono Story. “One of these difficulties always seems to involve a giant revolving mirror-ball lemon.”

“Cohl assumed that the whole tour would be a sellout, but he was dealing with a band that is out of touch with reality,” an anonymous promoter told Chicago rock journalist Greg Kot. “Say you’re an American kid reared on guitar rock and U2 is your favourite band, only U2 comes out a couple of years ago with a track that has [opera star Luciano] Pavarotti on it, and then puts out a dance track as the first single from the new album. Then they put a stadium show on sale for 50 bucks.”

Huge costs The huge costs of mounting the tour was acknowledged by Bono when the band arrived at a (less-than-capacity) Seattle Kingdome in December. “If we’re through here the next time, I think it’s gonna be something very different because, eh, I don’t think we’ll ever be able to afford to do this again. You know what I’m saying.”

We thought because there was so much discussion about the biggest tour, the biggest lemon, the biggest this, the biggest that, we thought we’d have some fun with that The whiff of farce continued even as the kinks were ironed out. What should have been a triumphant concert at Sarajevo’s Koševo Stadium that September became a huge challenge as Bono lost his voice; elsewhere on the European leg everyone’s worst fears came to pass as the lemon indeed break down, trapping the musicians inside on several occasions (they would play three Irish dates, in Belfast’s Botanic Gardens on August 26th and at Lansdowne Road on August 30th and 31st).

U2 didn’t become the biggest band the world without being self-aware, and they would later reflect that PopMart had misjudged their audience’s expectations – especially in their heartland of America.

“I think we did it to ourselves,” said Bono. “We thought because there was so much discussion about the biggest tour, the biggest lemon, the biggest this, the biggest that, way in advance of the tour, we thought we’d have some fun with that. Maybe we shouldn’t have. The reason people come to see us in the end is to hear our songs.”

Yet far from breaking U2, the setbacks merely made them more determined. They would revert to their core musical values and classic sound with their next album, 2000’s All That You Can’t Leave Behind, and reclaim their position as princes of stadium rock. Everything they have since achieved – two nights at Slane, a run of shows at Croke Park, the present tour – arguably flows from PopMart. They failed big and came back stronger.

And besides, every rock band should occasionally embrace the inherent ludicrousness of what it is they do. U2 have been many things through their 40 years – PopMart was the first and presumably last time they were screamingly silly. Appearing beside Bono on The Late Show with David Letterman early in the tour, drummer Larry Mullen Jr put it succinctly.