Paul McCartney's first solo No. 1 single actually harkened back to the way he worked toward the end of his time with the Beatles.

He'd been the principal architect of a medley that dominated the second side of 1969's Abbey Road, the last album completed by McCartney's old group. Originally titled "The Long One," it featured a series of joined song snippets. John Lennon would later trash the concept as nothing more than a desk-clearing exercise, but something sparked for McCartney creatively.

His debut, 1970's McCartney, followed a more stripped-down, personal path – but then came "Uncle Albert/Admiral Halsey," a technicolor outburst of sewn-together ideas with ever-shifting cadences, styles, collaborators and melodies. So, basically it was the Abbey Road assemblage, taken to a fizzy kitchen-sink zenith. "It's a bit surreal, but I was in a very free mood, and looking back, I like all of that," McCartney told Mojo in 2001. "It must have freaked a few people, 'cause it was quite daft."

He took inspiration from a project that arrived a few years before Abbey Road, producer Mark Wirtz's A Teenage Opera.

"It had a couple of songs where there were different sections all put together. It wasn't a usual rock 'n' roll record," McCartney said in 2021 Q&A for his official website. "This was more operatic in its form, and I always liked that. You sometimes want to change something, you want to write a ballad or you're feeling a rocking thing, or sometimes a folk thing and then you want to put them together. It's a format that I really enjoy writing, because it allows you to stretch."

Things didn't start out that way, actually. McCartney began working on the song in November 1970 at Columbia Studios in New York, with a group that included guitarist David Spinozza. McCartney then basically started over the following January, working in multiple studios with future Wings members Linda McCartney and Denny Seiwell, guitarist Hugh McCracken, George Martin, the New York Philharmonic Orchestra, a four-piece brass section and jazz bassist Ron Carter, among others.

It took an army, and overdub sessions stretching into April 1971, to complete McCartney's outsized vision for "Uncle Albert/Admiral Halsey."

Listen to Paul McCartney's 'Uncle Albert/Admiral Halsey'

Lyrically, he wanted to explore the widening generational divide, while echoing earlier character studies from the Beatles era. McCartney weaved childhood memories of his own Uncle Albert with fictional ideas based on a World War II-era U.S. Naval officer, Fleet Admiral Bill Halsey Jr. Albert Kendall had worked as a clerk for McCartney's father at a local cotton merchant before marrying Jim McCartney's sister, Milly.

"When I came to write 'Uncle Albert/Admiral Halsey,' it was loosely about addressing that older generation, half thinking: 'What would they think of the way my generation does things?'" McCartney said in Wingspan: Paul McCartney's Band on the Run. "That's why I wrote the line 'We're so sorry, Uncle Albert.' There's an imaginary element in many of my songs – to me, Admiral Halsey is symbolic of authority and therefore not to be taken too seriously."

It was fitting then that McCartney proceeded to break every rule in the studio.

"Uncle Albert/Admiral Halsey" actually starts in a perfunctory enough manner, with a pillow-y orchestral accompaniment later revealed to have been arranged by Martin, the Beatles' former producer. McCartney conducted the orchestra himself, during sessions at A&R Studios in New York.

Then he began constructing a quilt of idea fragments and sound effects: Rain and thunder crackled overhead, courtesy of environmental recordings reportedly captured from the edge of a cliff by studio assistant Armin Steiner. McCartney mimicked a tinny phone conversation by speaking through a high-pass filter, then had emerging bebop talent Marvin Stamm perform a flugelhorn solo to connect the song's two halves.

"'Uncle Albert' was a little message to my real Uncle Albert ... like a tongue-in-cheek apology," McCartney said. "And then with 'Admiral Halsey,' well, it just all went mad after that when he entered the picture. Again, we come back to the word free: It was very free, and that made this record very enjoyable."

Along the way, sections repeat (the "hands across the water, hands across the sky" refrain) while others appear only briefly ("live a little, be a gypsy, get around"). Even the brief wordless outro has two distinct elements, as an Americana-inflected backing gives way to the segue into "Smile Away," the next track on the album that became 1971's Ram.

With so much going on, it's easy to miss the brilliance of the horn players, though that was corrected with McCartney's sweeping instrumental version on the 1977 album Thrillington, which featured easy-listening versions of Ram's songs. Assistant engineer Dixon Van Winkle later admitted that he was "surprised when the record went so big" but praised the results, which he said had "the feel of an overture."

Listen to the Thrillington Version of 'Uncle Albert/Admiral Halsey'

McCartney's creative freedom extended to his collaborators, as McCracken came up with a guitar figure on the spot and Linda made key contributions to the tune's inventive vocal approach.

"Uncle Albert/Admiral Halsey" represented a "breakthrough in our musical relationship," the late McCracken told Mix magazine. "Paul is a genius. He sees and hears everything he wants, and would give specific instructions to me and the drummer. But he didn't know what he wanted the guitar part to be like on this song. I asked him to trust me, and he did."

Studio engineer Tim Geelan was particularly taken by the "sweet" interplay on the mic between Linda and Paul McCartney, as they improvised in call and response, created funny accents and then turned loose these soaring vocalizations. "Linda actually came up with some parts on her own," Geelan later remembered. "The entire backing vocals on 'Uncle Albert/Admiral Halsey' consists of the two of them."

Linda was ultimately listed as a cowriter on the song and also received a coproducer nod. The completed Ram album was credited to Paul and Linda McCartney, as well.

"Looking back at the records we made together, I think our harmonies were a really individual sound and a very special sound," McCartney said on his website. "Probably because she wasn't a professional singer, that gave her an innocence to her tone that comes through on the records. I'd be singing 'hands across the water' and she'd echo 'water, water' and do this funny little American accent, and we'd put it in! We were having fun."

Released on Aug. 2, 1971, as the first single from Ram, "Uncle Albert/Admiral Halsey" was certified gold just a month later and then subsequently earned a Grammy for Best Arrangement Accompanying Vocalists. But its legendary complexity ended up having a downside: McCartney has never played the song in concert.

"People keep requesting 'Uncle Albert,'" he told Rolling Stone in 2013. "It'd be great to do, but it's just a little bit of a challenge to learn, 'cause these are not 12 bars. But once you get them, and once you do them right, they kind of feel like 12 bars. That's the trick."

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