The Electric Light Orchestra had actually lost money on their most recent tour, a grandiose jaunt that featured a giant replica of their iconic album-cover spacecraft. They'd also reached the end of a creative road with the out-sized construction – and success – of 1977's platinum-selling Top 5 smash Out of the Blue.

It was time to cut back – in this case literally. Discovery arrived on May 31, 1979, with a streamlined sound, and a winnowed-down lineup.

"I just lost my way, totally," Jeff Lynne told Rolling Stone in 1990. "In the beginning, ELO was supposed to be very avant-garde, very off the wall. And then, once I started having hits, it drifted from that. Suddenly, the record companies and managers were clamoring for hits. And I tried to cater to the fuckers. And it grew into this monstrous thing that I didn't want. I got to feel trapped, and I didn’t have a clue as to what was going on. It was a fuckin' drag.”

He started by trimming the lineup to a foursome also featuring drummer Bev Bevan, keyboardist Richard Tandy and bassist Kelly Groucutt. Discovery became the first ELO project without an orchestral component, marking the departures of Mik Kaminski, Hugh McDowell and Melvyn Gale.

ELO engineer Reinhold Mack played a key role in this shift. At one point, he told Lynne, "Let's do away with the strings, let's do away with the choirs and let's just boogie out for a night."

Bevan was also itching to try a more straight-ahead sound. "I got bored with it too," he told the Dayton Daily News in 1979. "In the studio, it's very restricting to work with this band. ... I've tried doing more drum fills to liven it up, but when you put the orchestra and choir on top, it starts to sound a mess – so I have to keep it real simple. I've gotten to the stage where I don't even enjoy recording anymore. It's so mechanical."

Watch ELO's 'Don't Bring Me Down' Video

Then Lynne started trying something musically, a sound associated with contemporary acts like the Bee Gees rather than with the Beatles, ELO's most celebrated influence. The band's disco period was underway – and it started out with a bang. All backing tracks were laid down in a matter of days, once the group gathered for sessions in March and April 1979. After that, a massive post-production process got underway before Lynne finally filled in the lyrics.

"When everything was overdubbed to the hilt and the tracks were completely full, then Jeff would say, 'Okay, I'll have a shot at it,' and start singing," Mack told Sound on Sound in 2013. "That's just the way he worked. There weren't any guide vocals. In fact, the backing vocals would almost always be recorded before the lead vocal, which was the last thing to go on."

This abbreviated time frame would seem to indicate that they'd become a tighter-knit group. But Discovery – and, more importantly, ELO – had very much become a Jeff Lynne presentation. The problem was, nobody else knew just what his larger plan was.

"It was all inside Jeff's head,” Mack explained. "He'd tackle the backing line by line, saying, 'This goes here,' and 'Let's put a harmony on that.' Then I might say, 'Can you do a descending high harmony?' and he might say, 'Oh yeah, that's a pretty good idea! Let's try it.' Either it would be retained or he'd come up with something completely different, and the whole would evolve out of whatever he had in his mind."

The album's detours into the funk-infused dance music of the day ("Shine a Little Love," "Last Train to London") led Tandy to memorably quip that they should have called it Disco Very. Still, Bevan made no excuses.

"People say our music is a lot more commercial now," he told the Chicago Tribune in 1979. "Actually, we're not any more commercial now than we were five years ago, when we did the Eldorado album. If you want to talk about our first couple of albums, okay, those were less commercial. But since around 1974, we've been doing stuff in the same vein. It's just that we've gotten this mass acceptance now and people hear our stuff on the radio continually and they get the impression we've suddenly become a commercial band."

Listen to ELO's 'The Diary of Horace Wimp'

Lynne's interest in disco sounds didn't spring from trips to the hottest dance clubs of the day. Instead, it went all the way back to his youth.

"Yeah, I went to Studio 54 once," Lynne told Billboard in 2015. "It was all right, I suppose. It was full of film stars and all that. I just liked the four-to-the-bar basically. The bass drum going bang, bang, bang, bang."

And that wasn't the sum total of Discovery anyway. The project also made room for more straight-ahead rockers ("On the Run," "Don't Bring Me Down"), an underrated ballad ("Need Her Love") and a few magical trips back to their layered original sound ("The Diary of Horace Wimp," "Wishing," "Midnight Blue"). "Don't Bring Me Down," a Top 5 smash in the U.S. as well as in the U.K., was actually one of the last songs they attempted. Mack created a loop of two bars of drums from "On the Run," then altered the tape speed to get a booming rhythm.

"It's a great big galloping ball of distortion,” Lynne said in the liner notes to a 2001 reissue of Discovery. "I wrote it at the last minute, 'cause I felt there weren't enough loud ones on the album. This was just what I was after.”

The song, ELO's biggest-ever Billboard hit, helped Discovery streak to double-platinum sales. "Shine a Little Light," the lead single, became a Top 10 song on both sides of the Atlantic. "The Diary of Horace Wimp" and "Confusion" / "Last Train to London," a double A-side, both reached No. 8 in the U.K., marking the first time four Top 10 songs had ever emerged from one album.

Watch ELO's 'Shine a Little Love' Video

There were those who chafed when the new lineup premiered on Discovery. Confusingly, Kaminski, McDowell and Gale appeared in promotional videos for the record, even though they hadn't participated in its creation. ("The guys in the string section were upset about it," Bevan admitted to the Daily News. "I don't blame them. It's embarrassing for them.") Still, the Electric Light Orchestra seemed to have managed this early transitional period with ease.

Behind the scenes, however, Lynne's role became ever more central. Groucutt was gone after a couple more albums. Eventually, Lynne would resort to releasing records under the ELO banner with little more than an occasional contribution from Tandy – or anybody else. In the meantime, he dabbled in movie work, turned ELO toward synth-pop and tried a concept album. The strings stayed gone.

"Having a 30-piece string section was fine for the first three times, albums-wise," Lynne told the Quietus in 2015. "I'd be going, 'Oh great! Strings today!' But after that, it became, 'Oh, strings today. So fed up with these fucking strings.'"

Their last tour as a band was in 1982; the Electric Light Orchestra split after a quick run of shows some four years later. When the group reconvened in the new millennium, it was no longer a group at all, but rather a vehicle for Lynne's solo work.

By then, ELO's most familiar in-concert prop had long since met its own cruel fate. "The spaceship," Bevan mused in that 1979 Chicago Tribune interview. "I think it got broken up for scrap. A rather inglorious end to its career."