As the '60s came to a close, Spinal Tap were already something of a fixture within Swinging London's rock and roll elite. The release of Brainhammer, their now-illustrious fourth album, on April 1, 1970 showed Spinal Tap were evidently ready for even bigger things. The savvy men of Spinal Tap reasoned, in keeping with Bob Dylan's claim that the times were a-changin', that they must evolve or perish.

In fact, rolling with the constant changes of the decade's musical fashions had never proven all that difficult for leaders David St. Hubbins (vocals, rhythm guitar) and Nigel Tufnel (lead guitar, vocals). The pair first met as precocious street scamps involved in competing groups, the Creatures and the Lovely Lads, before joining forces as the Originals – which was soon changed to the New Originals. Then, with the arrival of steadfast bassist Derek Smalls and tall, blonde, geeky drummer John "Stumpy" Pepys, they became the Thamesmen, a post-skiffle, post-Beatles rear battalion of the British Invasion (if you will) who scored a modest domestic 1965 hit with "Gimme Some Money" (b/w "Cups and Cakes").

First, however, they'd have to endure the horrifying 1966 demise of drummer Pepys in a bizarre gardening accident – about which the least said, the better – and then the strange death of his short-term replacement, Eric "Stumpy Joe" Childs. (He choked to death a year later on vomit, though whose vomit, precisely, shall sadly remain a mystery until advances in modern vomit DNA testing may reopen this cold case). Nothing, however, could stop them from pursuing their dreams of rock stardom. Suffice to say that Childs was fondly remembered by Smalls for his "big hands, big feet, big heart. Small lips. Thin hair. Big ears. That really says it all."

Listen to Spinal Tape Perform 'Big Bottom'

By the dawn of the flower-powered summer of 1967, Tufnel, Smalls and St. Hubbins had recruited yet another talented percussionist in Peter "James" Bond, officially adopted the now-ubiquitous Spinal Tap moniker, and proceeded to almost conquer the globe with their enormous-selling single, "(Listen to the) Flower People."

Even the remarkable success of "(Listen to the) Flower People," however, would not safeguard Spinal Tap's future against rock's ever-shifting commercial tides. Subsequent singles like "(Again With the) Flower People" (from 1967's (Listen to the) Flower People and Other Favourites) and the title track to its 1968 follow-up, We Are All Flower People, fell short of expectations.

So, by the waning months of 1969, the group had once again entered the studio and, inspired by the rising wave of hard rock and heavy metal across the globe, they embarked upon a daring makeover of their sound for the resulting Brainhammer. As band biographer Peter Occhiogrosso put it, "The band hits its lumbering stride [here], moving with a lean, mean aplomb of a brontosaurus in fighting trim."

Released by Megaphone Records in 1970, Brainhammer delivered an impressive array of powerful anthems in its title track, the double entendre-laden "Lie Back and Take It," and triple-entendre-packed "Swallow My Love." The singularly enduring classic that ultimately pushed Brainhammer over the edge, and which continued to hold pride-of-place in every Spinal Tap concert for years, was "Big Bottom" with its innovative, three-way-bass attack. "I was dating a beautiful woman who went by the professional name of Lhasa Apso. Extraordinarily beautiful," St. Hubbins explained in a 1996 interview. To which Smalls retorted, "With one great exception," before David concluded "but that exception was the inspiration. End of story." Indeed, no one was questioning Spinal Tap's radical creative about face after hearing this poetic masterpiece, which was later covered by Soundgarden and others.

Looking back now, one can confidently say that Brainhammer was a genuine creative watershed that set the tone and template not only for Spinal Tap, but for hordes of like-minded heavy rockers to charge into the brand new decade. Along the way, Tufnel, St. Hubbins, Smalls and Bond (who spontaneously combusted onstage in 1977) released a string of landmark (and not-so-landmark) albums like Nerve Damage (1971), Intravenus de Milo ('74), The Sun Never Sweats ('75), and Rock 'n Roll Creation ('77), while facing some trials, but mostly triumphs. The turning point was Brainhammer.

See the Top 100 Albums of the '70s