Spanning the entire side of a vinyl album, the full-length version of “Autobahn” was defined by  the limits of recording technology in 1974. The second side features four shorter pieces, all electro-acoustic instrumentals. The two versions of “Kometenmelodie” (“Comet Medley”) were inspired by the Kohoutek comet, which passed close to Earth in 1973. The first is a doomy analog sound painting composed of sinister whooshes and whistles, the latter a joyous gallop of synth-pop fanfares over phased pneumatic percussion that lays the groundwork for Jean-Michel Jarre. “Mitternacht” (“Midnight”) plunges the listener into a clammy subterranean world of dripping water, metallic clanks and distant moans. But the LP ends on a hopeful note with “Morgenspaziergang” (“Morning Walk”), an ambient pastoral of tumbling flute and rippling piano, bubbling streams and larks ascending. This airy coda also reprises a melodic phrase from the early part of “Autobahn”, bringing the album full circle.

“All the tracks are like film loops, short films,” says Hütter. “‘Morgenspaziergang’ is what we wrote when we came out of the studio. We were always working at night, then in the morning, everything seems fresh and our ears are open again. Everything silent.”

Besides penning the lyric to “Autobahn”, Emil Schult also painted the LP cover image of a motorway sweeping up into a glorious mountain vista lit by an explosively vivid sunset. Hütter’s grey Volkswagen makes a cameo appearance. Both futuristic and nostalgic, the image blends contemporary Pop Art collage with the heroic landscape tradition of German Romanticism. A former student of artist Joseph Beuys, Schult’s idea was to “create something timeless, out of time,” like a vintage Bauhaus chair.

But the most iconic Autobahn sleeve image was an in-house addition by Kraftwerk’s UK label Phonogram. Based on a blue-and-white motorway logo, this instant design classic became the default sleeve on future reissues. Peter Saville would later claim the cover “advanced my notions of visual communication enormously” and directly inspired his groundbreaking work for Factory Records. The monochrome band photo on the rear of the album, taken by Schneider’s then-girlfriend Barbara Niemöller, initially featured Schult alongside Schneider, Hütter and a madly grinning, hippy-bearded Röder. But Schult was later given the unenviable task of superimposing Flür’s face onto his own body to mark the percussionist’s arrival as a full-time Kraftwerk member. A very Orwellian touch.

Released in Germany on the Phillips label in November 1974, Autobahn was a striking sonic progression for Kraftwerk, distancing them from their hairy Krautrock peers. “I was very impressed by the sound,” recalls Rother, “but I would not have wanted to make music like that. There was not enough flesh and blood in it. It was a very conceptual approach to music.”

To promote the release, the band began looking to expand their live lineup. Rother was invited to rejoin, but he was too busy with Harmonia and Neu!. Eventually Hütter and Schneider recruited the classically trained Karl Bartos, who was studying at Düsseldorf’s Robert Schumann Conservatorium. Moving into Schult’s Berger Allee apartment, Bartos and Flür brought a hint of marketable pop-star glamour to Kraftwerk. Both became long-term fixtures in the band, despite being hired hands on a monthly wage. “I would never have accepted a deal like that,” Rother insists. “We didn’t even get to that point, but I would have just laughed at them. Maybe it’s just the old hippy in me, not wanting to accept that you can handle music with other people like a business.”

Meanwhile, across the Atlantic, interest in Kraftwerk was building. Noting that imported Kraftwerk albums were selling pretty well through Jen Records of New Jersey, the band’s US label Vertigo gave Autobahn an official release early in 1975. They also made the bold decision to cut the title track down from 22 minutes to 31/2 minutes and promote it as a novelty radio single. It climbed to No 25 on the US Billboard chart and No 11 in Britain.

Ira Blacker, a tour promoter and manager who had been instrumental in breaking foreign acts like Rod Stewart and Rush in America, spotted a gap in the market for German artists. “I used to hit the import bins in Greenwich Village to get the Euro imports,” Blacker says. “I bought Kraftwerk before it ever came out in America, Neu!, Harmonia, Tangerine Dream, Klaus Schulze, different things. So I took a trip to Germany, made contact with a bunch of bands.”

Blacker signed a deal to represent Kraftwerk in the US, also steering them to a new contract with EMI. On first impressions, he found Hütter and Schneider “personable, upper middle class guys. Bright, intelligent conversation, a lot of joking around. I went to visit them in Düsseldorf and I gave them a ‘sieg heil’ at the gate… they got the joke.”

Blacker booked Kraftwerk for a substantial spring tour of the US and Canada. Initially 22 dates, with more added. They drove through blizzards, sunned themselves beside Hollywood pools, played on Broadway, visited Disney World and even got to see The Beach Boys play live. Bootleg recordings and TV clips from this tour capture a band in transition from experimental boffins to left-field pop stars, confounding US rock fans with their electro-mechanical tone poems full of drones, crackles and ambient fuzz tones. “It was totally avant-garde,” says Blacker. “It was electronic. Not disco… disco hadn’t discovered Kraftwerk at that point. But they were well received wherever they went. I did a lot of announcing for the band, bits and pieces in German. I was onstage in Chicago and a few kids started yelling ‘rock and roll!’ Ha! They got their ovations… they did well.”

“They did not understand,” recalls Flür. “However, it was not necessary to understand it, they enjoyed it because it was so new and experimental. During the first US tour, we had problems with equipment. The PAs in the halls were not designed for our massive analog sounds and many speakers burst.”

By the time they flew back to Düsseldorf in June 1975, Kraftwerk were international chart stars. Top 10 in Germany, Autobahn rose to No 5 in the US and No 4 in Britain. The band’s live schedule began to fill up, with Blacker booking a debut UK tour for September. But Hütter recalls a chilly reception at home. “We toured with Autobahn for the first time outside Germany,” Hütter says. “A long time in America, then a shorter tour in England. But Germany had to be cancelled, as there was no interest. The record was a big success but nobody could imagine it live – is this a studio record? Or electronic?”

Conversely, Flür recalls positive reviews from America and Britain having a knock-on effect at home. “In Germany artists are often not well regarded unless they’ve scored great achievements abroad,” he says. “Our success in the US finally brought good headlines in the German newspapers.”