"I think we were pretty high when we made a lot of that record," Geddy Lee said of Caress of Steel in the Rush documentary, Beyond the Lighted Stage. "And it sounds like it to me."

Indeed. On one hand, the Canadian trio's third LP, which was released on Sept. 24, 1975, was a stoned leap forward. It built on their foundation of virtuoso hard-rock with the mystical imagery and progressive suite structures that dominated their '70s work. Rush are one of the great prog-rock bands, and Caress of Steel is their first real prog album. But despite its importance, it remains the black sheep of their catalog with its meandering instrumentals and shrieked vocals; even the band members feel uncomfortable listening to it decades later.

"That whole Caress of Steel period is stuck in a strange and funny moment in our history," Lee told Rolling Stone in 2014. "I really don't know how that would stand the test of time."

In June 1975, the band entered Toronto Sound Studios, intent on expanding their musical ambitions – and side-stepping the obvious critical comparisons. "We've been influenced by everyone who's good," Lee told St. Catharines Standard that year. "We're constantly being compared to Led Zeppelin, but that's only because my voice sounds like Robert Plant's – it's an unfortunate coincidence."

Working closely with producer Terry Brown, the trio – bassist-singer Lee, guitarist Alex Lifeson, drummer-lyricist Neil Peart – dove headfirst into fantasy storytelling, black-light psychedelia and heavy riffs. The results were admirably eclectic, ranging from the thundering march of "Bastille Day" to ethereal epic "The Necromancer," which references Tolkien, Satan and themselves, both in the name-checking of "By-Tor & the Snow Dog" and the story involving "three men from Willowdale."

Caress is almost unrivaled in its blend of brilliance and stupidity. "Lakeside Park" is lite-prog excellence: funky Lee bassline, blistering Lifeson guitar solo, sing-along chorus. Then there's "I Think I'm Going Bald," which recycles a generic blues-rock riff and lyrics that are self-explanatory. The closer, "The Fountain of Lamneth," condenses that insanity down to 20 minutes – for every mesmerizing passage (Lifeson's nylon-string guitar), there's a nails-on-chalkboard Lee screech.

"We played it in our van for [Kiss' Paul Stanley] one night [on tour], and you could see that he just didn't get it," Lifeson recalled in Beyond the Lighted Stage. "A lot of people didn't get it. We wondered if we even got it!"

The band's cult following continued to grow in small increments, but the album flat-lined their commercial momentum. It barely cracked the Billboard 200 at No. 148 and set the table for Rush's self-deprecatingly dubbed "Down the Tubes" tour.

"That was a depressing time," Lee told The Guardian in 2011. "You'd pull up at a venue and they didn't even expect you there; it was humiliation after humiliation. Your shoulders start to slump, and you wonder why you're playing a rock club in Oklahoma City on a wet Tuesday night. The label and the management wanted us to follow a straight path, but we went hard left. We were convinced we would be dropped and end up back home playing bars."

Despite its inconsistencies, Caress of Steel was a crucial step in Rush's evolution, setting the foundation for their breakthrough LP, 1976's 2112.

"'The Fountain of Lamneth' on Caress of Steel, was really our first full concept song, and '2112' was an extension of it," Alex Lifeson told Guitar World in 2008. "That was a tough period for Rush because Caress of Steel didn’t do that well commercially, but we were really happy with it and wanted to develop that style."

"A lot of the early stuff I'm really proud of," Lee told Raw magazine in 1993. "Some of it sounds really goofy, but some of it stands up better than I gave it credit for. As weird as my voice sounds when I listen back, I certainly dig some of the arrangements. I can't go back beyond 2112 really, because that starts to get a bit hairy for me, and if I hear 'Lakeside Park' on the radio I cringe. What a lousy song! Still, I don't regret anything that I've done!"

Rush Albums, Ranked Worst to Best

This Day in Rock History: September 24