Just how good is London Calling, the landmark third album by English rockers The Clash? Rolling Stone ranked the double LP #1 on its list of the “100 Best Albums of the Eighties,” even though it technically came out in late 1979. To be fair, the magazine was using the American release date of January 1980, but the rating speaks to the timeless quality of the music.

Mixing a variety of musical genres, including reggae, ska, rockabilly, and R&B, London Calling is the sound of punk’s most ambitious band driving full speed through genre barriers and claiming its rightful place in the rock ‘n’ roll pantheon. To celebrate the album’s 40th birthday, here are 10 facts about the undisputed masterpiece from “the only band that matters.”

1. London Calling was written in seclusion.

After parting company with manager Bernie Rhodes, a key player in the creation of London’s punk scene, The Clash needed a new place to rehearse. They found the perfect location in “Vanilla Studios,” a dingy room in a converted auto garage in London’s Pimlico neighborhood. What the studio lacked in amenities, it made up for in privacy. Sequestered from the rest of the world, The Clash were free to explore their wide range of musical influences and push their artistry to the next level. During breaks, they’d head to a local playground for spirited games of soccer that sometimes involved visiting execs from CBS Records.

2. The Clash may have seen London Calling as their "last shot."

Mick Jones, Topper Headon, Paul Simonon, and Joe Strummer in Monterey, California during the band's "Pearl Harbor '79" tour.George Rose/Hulton Archive/Getty Images

Nowadays, The Clash are critically revered Rock and Roll Hall of Famers often discussed in the same breath as The Beatles and the Rolling Stones. But in 1979, when they were strapped for cash and newly split from Rhodes, the band faced a very uncertain future. “Economically, we were really tight at the time,” Clash frontman Joe Strummer told Melody Maker. “This album woulda been our last shot, never mind if we didn't have the spirit for it, which we did.” Strummer added: “Desperation, I’d recommend it.”

3. Producer Guy Stevens was a wild man in the studio.

When The Clash hired Guy Stevens to produce the album, the eccentric Englishman was many years removed from his glory days promoting American R&B in the ’60s and working with UK rockers Mott the Hoople in the early ’70s. Plagued by drug and alcohol problems, Stevens was, by all accounts, washed up. But he turned out to be the perfect man for the job.

Using a process that engineer Bill Price described as “direct psychic injection,” Stevens would do things like throw chairs and ladders against the wall to inspire emotional performances. Once, he poured a bottle of red wine onto the studio’s piano—while Joe Strummer was playing it. Non-virtuoso Clash bassist Paul Simonon was especially fond of Stevens. "He made me feel really at ease,” Simonon said. “If I played wrong notes, he didn't care."

4. London Calling's biggest U.S. hit wasn’t listed on the album's sleeve.

London Calling gave The Clash their first American hit, “Train In Vain,” which reached #23 on the Billboard Hot 100. Guitarist Mick Jones wrote the uncharacteristic love song about his split with Viv Albertine of fellow British punk band The Slits. Jones knocked it out in one night, and the band recorded it the next day, just as the album sessions were wrapping and the roadies were packing up the gear.

Named for the song’s driving rhythm and the “lost” feeling evoked by the lyrics, “Train In Vain” was originally intended for the music magazine NME as a flexi-disc giveaway. When that deal fell through, The Clash stuck the song at the end of their just-completed album. Unfortunately, the artwork had already been printed, so “Train In Vain” wasn’t listed on original pressings. It was a “secret track” that didn’t stay secret for long.

5. The Clash tricked CBS into making London Calling a double album.

Throughout 1979, The Clash butted heads with their label, CBS Records, about the retail price of their albums. The notoriously fan-friendly band wanted London Calling to be a double LP that would sell for the same as a single LP—an idea the label wasn’t really into. The Clash struck a deal whereby they could release a single album with a bonus 7” single, as they’d done with the American pressing of their 1977 debut album. After CBS agreed to this, The Clash pushed for the bonus single to be a 12” containing eight songs. With the last-minute inclusion of “Train In Vain,” the “bonus single” contained nine songs. London Calling was now a double album, and sure enough, it retailed for the same price as a single album. “I’d say it was our first real victory over CBS,” Strummer told Melody Maker in December 1979.

6. London Calling features three cover songs.

In addition to being some of the best songwriters of their generation, The Clash's band members were terrific interpreters of other people’s music. Nowhere is that more apparent than on London Calling. After throwing down the gauntlet with the opening title track, the boys speed through a version of “Brand New Cadillac,” a 1959 B-side by British rockabilly artist Vince Taylor. The Clash were also enthusiastic fans of Jamaican music; they opened side three with the rollicking ska of "Wrong ‘Em Boyo,” a retelling of the Stagger Lee legend originally done by The Rulers. Finally, they closed out the original 18-song tracklist with a remake of reggae singer Danny Ray’s 1979 B-side “Revolution Rock.”

7. London Calling's title track was partially inspired by a nuclear accident.

In the chorus of album opener “London Calling,” Joe Strummer sings, “A nuclear error, but I have no fear.” That line was inspired by the partial meltdown at Pennsylvania’s Three Mile Island Nuclear Generating Station in March 1979. It’s one of many apocalyptic scenarios Strummer references on “London Calling,” a song that also refers to food and energy shortages, climate change, police brutality, and more. (The original title was “Ice Age.”) “We felt that we were struggling, about to slip down a slope or something, grasping with our fingernails,” Strummer said of the doomy anthem. “And there was no one there to help us.”

8. A biography of screen star Montgomery Clift inspired The Clash's “The Right Profile."

In A Riot of Our Own, his excellent 1999 account of working with The Clash through the late 1970s, road manager Johnny Green recalls Guy Stevens sharing a biography of Montgomery Clift, the American actor known for his roles in films like Red River and A Place In the Sun. Clift suffered a serious car accident in 1956 that altered the left side of his famously handsome face, which basically killed his career. According to Green, the book passed between all four members of The Clash, ultimately inspiring “The Right Profile,” a tragicomic look at Clift's plight.

9. London Calling features the same horn section heard on a cheesy ’80s classic.

The Clash used many session musicians on London Calling, most notably The Irish Horns, a foursome comprising trombonist Chris Gower, trumpeter Dick Hanson, and saxophonists John Earle and Ray Beavis. The quartet were typically billed as The Rumour Brass, as they made their name playing with Graham Parker and The Rumour. After leaving their mark on London Calling tracks like “The Right Profile” and “Revolution Rock,” The Rumour Brass played on a plethora of recordings, including The dB’s’ 1982 album Repercussion and Katrina and the Waves’s eternal ’80s classic “Walking On Sunshine.”

10. London Calling's album cover pays homage to Elvis Presley.

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In their classic tune "1977," The Clash declare, “No Elvis, Beatles, or The Rolling Stones!” They were adopting punk’s year-zero, kill-your-idols mentality, but in reality, they were lovers of rock ‘n’ roll mythology and huge fans of all three legends they appeared to diss. This was made clear by artist Ray Lowry’s London Calling cover design.

With its black-and-white photo and neon green and pink lettering, the layout pays tribute to Elvis Presley’s 1956 self-titled debut album. There is, of course, one key difference: Whereas Elvis is seen pointing his guitar upward, The Clash opted for a photo of Paul Simonon slamming his bass down into the floorboards at The Palladium in New York City. Fans long believed that photographer Pennie Smith snapped the iconic shot on September 21, 1979, but evidence suggests Simonon actually smashed his bass a day earlier.