During the 1976 heavy metal was still very much in its larval stage. Black Sabbath, five albums in already, was laying down molten lead plugged into an overdriven guitar amp. While they were certainly heavier than anything else at the time, their sound was still heavy rooted in stoner blues rock, just with an ungodly amount of distortion.

That’s where Judas Priest comes in. Two years previous they dropped their debut Rocka Rolla, an eclectic if confusing mix of Led Zeppelin, Black Sabbath and Jethro Tull. We have seen many cases of a band’s debut being their best work and said band subsequently attempting to recreate that magic to no avail. For Judas Priest, Rocka Rolla shows a young band with promise but no focus. Who knew they would become one of the standard-bearers for heavy metal?

There were several legendary songs left on the cutting room floor during this process for the sake of accessibility: “The Ripper,” “Tyrant,” “Genocide” and “Victim of Changes,” which certainly contributed to the unfocused nature of Rocka Rolla. Still, their debut album is a fascinating glimpse into how far Judas Priest has come today.

It is also a fascinating study to measure how far they came in only two years. On this day in 1976, Judas Priest released their sophomore album Sad Wings of Destiny, which has been universally acclaimed as one of the finest releases in metal music history. While Black Sabbath was responsible for creating heavy metal, Sad Wings of Destiny was responsible for giving it its signature sound. Indeed, this album can be considered the first “true” heavy metal album.

Remember those legendary tracks mentioned before? All four of them come rearing their heads on Sad Wings of Destiny and have been long-time staples in the Judas Priest discography. “Victim of Changes” is about as ferocious an album opener as can be in 1976, opening with twin harmonies from guitarists Glenn Tipton and KK Downing before settling into a catchy blues lick. The eight-minute epic is a roller coaster, constantly building and slowing in intensity and tempo. The middle section has a particularly fun guitar duel, as well as patented shrieks by vocalist Rob Halford.

“The Ripper,” as the name implies, is a blisteringly fast concept song about Jack the Ripper, with Halford shrieks galore and wicked ripping guitars. “Dreamer Deceiver” is a slower blues-styled ballad that takes the foot off the gas, and is perhaps one of the greatest examples of Halford’s impressive vocal range.

“Deceiver” is almost the opposite of “Dreamer Deceiver,” a rocking bass-driven song with an infectious main riff. Ian Hill’s bass, which is tuned in a higher octave than the guitars, sounds particularly groovy in this song. There’s the keyboard-laden “Prelude,” as well as “Tyrant,” a proto-thrash attack between Tipton and Downing. This song contains perhaps Hill’s greatest bass line in his career.

“Genocide” is another aggressive mid-paced tune, which really picks up in a frenzied fury near the end of the song. Is Halford… rapping? …Almost? This is your reminder that the year is 1976. The next song “Epitaph” is the second of two ballads on Sad Wings of Destiny. It has a great piano performance from Tipton with an equally impressive lyrical performance from Halford.

This ballad sets the stage for speedy closer “Island of Domination,” which has a particularly interesting sequence where the rhythm breaks down in the middle of the song, which comes roaring back in the form of an evil, Black Sabbath-y riff, before the rest of the song picks back up. Halford’s vocals during this part of the song sound almost soul-like. He definitely could have made it on Motown if he tried.

If you want to hear a slightly more “modern” and polished sound of some of these songs, I highly recommend checking out Judas Priest’s 1979 live album Unleashed in the East. Not only is it one of the greatest live albums ever made, but all the tracks from Sad Wings of Destiny that make an appearance sound truly incredible.

Drummer Alan Moore delivers a solid performance, but ultimately this would prove to be his only studio recording with the band before leaving.

The lyrical topics are diverse social commentary, ranging from torture, abuse of power, oppression and the discrimination Halford felt as a homosexual (over two decades before he officially “came out”).

Judas Priest had many firsts, and one of them was their twin lead guitar attack. No other band in the 1970s would have been able to pull off the guitar acrobatics seen in “Tyrant” and “Genocide.” Sad Wings of Destiny was a legendary release that played an undeniable role in defining what heavy metal would evolve into. Although it was just one of the many jewels they have had across their storied career, it was arguably their most important.