The Mark II edition of Deep Purple is generally agreed to be the ultimate version of the hard rockers. The lineup of singer Ian Gillan, guitarist Ritchie Blackmore, bassist Roger Glover, keyboardist Jon Lord and drummer Ian Paice is responsible for many of the British group’s most beloved albums (In Rock, Machine Head) and songs (“Smoke on the Water,” “Highway Star”). This might have also been the busiest lineup in Deep Purple’s history.

Between 1970 and 1973, this quintet recorded and released four studio albums, put out a double-live classic (Made in Japan) and released a couple of non-album singles (“Black Night” and “Strange King of Woman”) – all while relentlessly touring Europe, North America and Asia. As the fall of 1972 approached, Deep Purple were burned out, and yet their punishing schedule had made the rockers as popular as ever. The band’s managers, Tony Edwards and John Coletta, wanted the group to continue to feed that popularity.

Using the Rolling Stones’ mobile recording truck – the same one Deep Purple had employed to record Machine Head in Switzerland – the band had begun work on a new album in July in Rome, between touring commitments. These sessions produced “Woman From Tokyo,” inspired by Deep Purple’s anticipation of their first tour of Japan in August. But, otherwise, this was kind of a bust. In terms of creativity, the band was running on fumes.

“We had just come off 18 months of touring, and we’d all had major illnesses at one time or another,” Gillan recalled more than a decade later. “Looking back, if they’d have been decent managers, they would have said, ‘All right, stop. I want you to all go on three months’ holiday. I don’t even want you to pick up an instrument.’ But instead, they pushed us to complete the album on time.”

Instead of taking a much-needed break, Deep Purple took the Stones’ mobile equipment to Walldorf, Germany, near Frankfurt, in October 1972. Blackmore felt that the sessions provided an opportunity for the band to rediscover its blues roots, after deciding that recent releases had “grown too ‘poppy’.” His guitar took on a bluesier sound throughout the sessions, the band encountered a blues workout on “Place in Line” and Gillan even did some scat singing on “Rat Bat Blue.”

But apparently there wasn’t much in the way of a creative discussion between Deep Purple’s guitarist and singer. Apparently, in 1972, they weren’t discussing anything.

“The last year of the band’s life, before ’73, I don’t think Ritchie or Ian Gillan spoke one word to each other,” Glover revealed in a BBC documentary. “They became two poles, because the more one would do it, the more the other would do it. And the more one got away with it, the more the other one was determined he was going to get away with it.”

With such friction in the band, Deep Purple often recorded their parts separately, cobbling together the follow-up to the massive hit Machine Head by overdubbing the different pieces. That method might have gotten the job done, but it lacked for the band’s chemistry, so evident on the live Made in Japan, released in the U.K. in December 1972 (and the next year in the U.S.).

Who Do We Think We Are, the seventh LP credited to Deep Purple, arrived in January 1973. The title was a reference to a Melody Maker interview with Paice (reproduced in the album artwork), in which the drummer discussed the hate mail that came to the group: “The angry ones usually start off. ‘Who do Deep Purple think they are … '” With a prominent riff, the album’s sole single “Woman From Tokyo,” became another radio hit for the band and coaxed the LP to No. 4 on the U.K. charts and No. 15 (with gold status) in the U.S. But the initially robust sales were also a carryover from the blockbuster success of “Smoke on the Water” and Machine Head. Save for “Woman From Tokyo,” Who Do We Think We Are is not one of Deep Purple’s most popular LPs with fans or critics, who comment on the effects of the band’s discord in their recordings.

Not long after the album’s release, during yet another tour, Gillan announced in a letter to the band that he would be leaving at the end of Deep Purple’s second Japan tour in the summer of 1973. Perhaps sensing an opportunity to radically shift the group’s sound, Blackmore suggested to Lord and Paice that they should replace Glover on bass. Before they could do so, Glover decided to leave Deep Purple with Gillan. Mark II’s last show of their original run came in June 1973 in Osaka, Japan.

“It was the biggest shame in rock ’n’ roll,” Lord said with the benefit of hindsight. “God knows what we would have become over the next three or four years.”

As such, Deep Purple brought on singer David Coverdale and bassist/singer Glenn Hughes and maintained much of their success before splitting in 1976. The Mark II lineup got a second shot when the five members reunited for more albums and more touring in 1984, though nothing on the scale of the band’s early ’70s pace.

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