Written, recorded and released over a period of just 10 days, John Lennon's "Instant Karma!" was a big seller, boasted one of rock's most inventive drum fills – and had sweeping implications for the Beatles.

Lennon felt certain that he had a hit as soon as the song was completed, so much so that (in keeping with its theme) he was determined to rush "Instant Karma!" out to the general public. Lennon would subsequently boast, in only a slight exaggeration, that he "wrote it for breakfast, recorded it for lunch and we're putting it out for dinner."

Fans ate it up. "Instant Karma!," released with the Plastic Ono Band in the U.K. on Feb. 6, 1970, shot to No. 5; two weeks later, on Feb. 20, 1970, it was issued in the U.S., where it reached No. 3. It was a Top 10 smash in several other countries as well, including Canada where it climbed to No. 2.

The only problem? The Beatles were ostensibly still together. In reality, they had been locked in a series of inner-band battles, to the point where tapes from a year-old return-to-roots project, initially titled Get Back, still hadn't been released. By the time it was all over, Lennon had handed the session tapes to "Instant Karma!" producer Phil Spector – a decision that would shatter the Beatles forever.

The song grew out of a conversation between Lennon, his wife Yoko Ono, Ono's former husband Tony Cox and Cox's wife Melinde Kendall, in which they had discussed the idea of ultimate fates happening in our lifetimes, rather than in the next. Lennon completed the thought on Jan. 27, 1970, recording an anthem-like exhortation that mankind join together to thwart these awful outcomes by living peaceably.

"Everybody was going on about karma, especially in the '60s," Lennon told David Sheff, "but it occurred to me that karma is instant, as well as it influences your past life or your future life. There really is a reaction to what you do now. That's what people ought to be concerned about. Also, I'm fascinated by commercials and promotion as an art form. I enjoy them. So, the idea of instant karma was like the idea of instant coffee: presenting something in a new form. I just liked it."

Lennon wrote  "Instant Karma!" in less than an hour. He called up George Harrison, hoping to quickly put the song to tape that same evening. Harrison then contacted Spector. "John phoned me up one morning in January and said, 'I've written this tune and I'm going to record it tonight and have it pressed up and out tomorrow – that's the whole point: 'Instant Karma,' you know,'" Harrison later remembered.

"So I was in. I said, 'Okay, I'll see you in town,'" Harrison added. "I was in town with Phil Spector and I said to Phil, 'Why don't you come to the session?' There were just four people: John played piano, I played acoustic guitar, there was Klaus Voormann on bass and Alan White on drums. We recorded the song and brought it out that week, mixed – instantly – by Phil Spector."

Watch John Lennon Perform 'Instant Karma!'

Billy Preston, who took part in the shelved sessions that would become Let It Be, appeared on organ. For White, a member of Lennon's recent ad hoc solo concert debut with the Plastic Ono Band in Toronto, it all came together in the blink of an eye.

"I was just waking up in the morning when I got a call from [longtime Beatles assistant] Mal Evans," White recalled in a 2014 interview. "He said John had just written this song and he wanted to record it today and release it next week."

The final of 10 takes was selected as the master and, in keeping with the Spector sound, a furious round of overdubs commenced. Three pianos (two acoustic, one electric) were added, with Lennon, Harrison, White and Voormann all taking part. A group of people from a nearby nightclub was invited in to provide the singalong backing vocals, with Harrison directing a ramshackle choir that also included manager Allen Klein. White added still more drums, bolstering a performance that already included signature improvisation.

“We all met at Abbey Road, and I had an idea of what I wanted to do," White said. "It was kind of one of those things where you are playing a rhythm, but when it comes to a drum break, you play in a different meter. It came naturally – and John said, ‘Alan, whatever you’re doing, keep doing it. It’s wonderful.’ There were only a few of us in there. He and I played piano overdubs afterward. ... Phil Spector liked to take multiple sounds and make them sound like one. He'd never put one tambourine on a record; he had to have 15 of them."

Spector completed things with an echo-filled mix that recalled Lennon's favorite Sun Records songs and showcasing White's imaginative asides in a way unlike any Beatles session that had preceded it. "Suddenly we went in the room and heard what he'd done to it," Lennon said later. "It was fantastic. It sounded like there was 50 people playing."

Though Lennon was still officially a member of the Beatles, "Instant Karma!" was, in fact, his third single to be released under the Plastic Ono Band banner. But unlike the others, this one – the first solo song by a Beatle to sell 1 million copies in the U.S. – definitively shifted the Fab Four's trajectory.

Spector eventually took over post-production of Let It Be at Lennon's behest. The results, which inverted the band's original back-to-basics aim with a typical Wall of Sound approach, created a final rift with Paul McCartney that effectively ended the Beatles. Two months after the release of "Instant Karma!," McCartney officially announced the split, and then released his self-titled solo debut album.

Spector would end up working on various projects with all of the Beatles – except for McCartney, who later stripped down Let It Be for a 2003 reissue. Lennon, meanwhile, performed "Instant Karma!" during a joint appearance with Ono on England's Top of the Pops on Feb. 11, 1970. The song was also part of Lennon's last full-length concert appearance, a two-show stop on Aug. 20, 1972, at Madison Square Garden.

His afternoon performance was released as part of Live in New York City six years after his 1980 murder. At the time of his death, "Instant Karma!" remained Lennon's only gold-selling single.

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