In April of 2010 I wrote the following:

"...The modern usage of "metal" in the musicological sense date back to 1968... This leads me to believe that no radio show can claim to have begun before the mid-1970s and truly have any metal music to air. So it is no surprise that few programs can be authoritatively dated to even the early 1980s."

So even having made a list [LINK] of very early and long-running metal radio programs, I supposed there could hypothetically have been a metal show that pre-dated the 1980s metal boom. But that the program could be no early than the mid 1970s. I have now found that radio program. But first a little etymology.

We can thank our favorite heroin addict William S. Burroughs for the origin of "metal" terminology. He used the words "heavy metal" in two books.  Published in 1962, The Soft Machine has a character known as "Uranium Willy, the Heavy Metal Kid". In 1964 he revisits the term in Nova Express with Insect People of Minraud with "metal music." Inspired by these books in 1967, the band Hapshash and the Coloured Coat  put out the album Human Host and the Heavy Metal Kids.
In this etymology "heavy" means profound and/or potent, a 1960s slang use of the word. In 1968 both Steppenwolf and Iron Butterfly prophetically used the word heavy in that context. The first confirmed use of 'metal' as an adjective to describe music appears in a review by Barry Gifford in an issue of Rolling Stone published in 1968. It described the band Electric Flag. But Lester Bangs writing for Creem Magazine in May 1971 used "heavy metal" to describe Sir Lord Baltimore which aligns more with the modern use of the term.

So in April of 1978 comes the program "The Vinyl Underground" hosted by Jeff Bender on WGTB. The program description in the Program guide reads as follows:

"Heavy-metal with a chrome edge-and buffed to a diamond-like shine by Jeff Benders eclecticism and tasteful choice of the very best (and some of the most obscure) hard rock produced. A real rock & roll alternative."

Bender previously co-hosted the program Hard Implosion with co-host Fred Cresce in 1976. This was probably more of a hard psychedelic rock program, but the sub-genre itself and the emphasis on "hard" in the name makes it a likely precursor to the metal radio programs that followed. By 1978 Cresce was hosting a program called Magic Carpet Ride, which leaned toward the psychedelic. But on Saturday nights at 9:00 PM he hosted another program. The description makes clear he too is using the term "heavy metal " in the Lester Bangs sense. The April program guide reads as follows:

"Some good party music to end the week with the accent on the heavy metal and just plain good old rock & roll. Please have plenty of speaker fuses handy!"

But thanks to Michael Manos, we have recordings of two episodes of Hard Implosion. One from December 29th of 1978, The other undated but due to the February release dates of the Judas Priest, and Alvin Lee albums, I believe it's from about that time. So we can examine these playlists and see that it bears out my original thesis as to the content.

[Note, Part 6 of the 12/29 tape is actually backsold on part 2 of the assumed Feb, 1978 tape so I think it's is incorrectly associated with that tape. I have transplanted it to it's assumed correct sequence.]

UNDATED TAPE (Assumed Feb, 1978)

Artist	Title	Album	Year
April Wine	Gimmie Love	Rocks!	1976
UFO	Lights Out	Lights Out	1977
Blue Oyster Cult	Dominance and Submission	Secret Treaties	1974
David Bowie	Diamond Dogs	Diamond Dogs	1974
Atlanta Rhythm Section	Cold Turkey, Tenn	Back Up Against the Wall	1973
Back Street Crawler	New York, New York	The Band Plays On	1975
Omega 6	Just a Bloom	Nem Tudom A Neved	1975
Moxy	Are You Ready	Riding High	1977
Moxy	Sailors Delight	Under the Lights	1978
Head East	Get up & Enjoy Yourself	Head East	1978
Montrose	Jump On It	Jump On It	1976
Judas Priest	Deep Freeze	Rocka Rolla	1974
Lou Reed	Andy's Chest	Transformer	1972
AC/DC	T.N.T.	High Voltage	1976
AC/DC	Ain't No Fun	Dirty Deeds Done Dirt Cheap	1976
AC/DC	It's a Long Way To The Top	High Voltage	1976
Van Halen	I'm the One	Van Halen	1978
Yesterday & Today	Fast Ladies	Yesterday & Today	1976
UFO	Highway Lady	No Heavy Petting	1976
Budgie	In the Grip of a Tyre Fitters Hand	Never Turn Your Back on a Friend	1973
Rainbow	Sixteenth Century Greensleeves	Ritchie Blackmore's Rainbow	1975
N/A	"Taking it Easy"?	N/A	N/A
Judas Priest	Better by You, Better Than Me	Stained Class	1978
Uriah Heap	Devil's Daughter	Return to Fantasy	1975
Black Sabbath	Paranoid	Paranoid	1975
Judas Priest	Saints In Hell	Stained Class	1978
Led Zeppelin	Dazed and Confused	Led Zeppelin	1969
Rush	Before and After	Rush	1974
Montrose	One Thing on my Mind	Montrose	1973
Motors	Whiskey and Wine	Motors	1977
Moxy	Wetsuit	Moxy	1975
Geordie	Can You Do It	Hope you Like it	1973
Steppenwolf	The Night Time's For you	For Ladies Only	1971
Lonestar	A New Day	Lone Star	1976

Notably on the February tape after a particularly metal-leaning set of songs Crese makes the prescient remark "We heard what I felt was a sound-alike set, where these three groups: Black Sabbath, Judas Priest and Uriah Heap sound the same to me, OK?... What did you think?"  None of these bands knew in 1978 that they were blazing a heavy metal trail that thousands of other bands would follow. In the intervening decades tens of thousands of new metal bands and a litany of new metal subgenres would be born. In that moment, Cresce is so close to realizing what we all now know.

On both tapes Fred Cresce does a nice professional job back-selling the songs so even though the tape starts at one song, he tells us what he aired in the prior 20+ minutes in order. It also helps me identify what are now fairly obscure songs in some cases. Consequently we get a bigger sample playlist.

DECEMBER 19th, 1978 TAPE:

Artist	Title	Album	Year
Journey	Mystery Mountain	Journey	1975
Rush	Hemispheres	Circumstances	1978
Three Man Army	What's My name	A Third of a Lifetime	1971
Blue Oyster Cult	ETI	Agents of Fortune	1976
Stepson	Rule in the Book	Stepson	1974
Montrose	Jump On it	Crazy for you	1976
James Gang	Cruisin' Down the Highway	Miami	1974
Sammy Hagar	Rock 'N' Roll Weekend	Sammy Hagar	1977
Captain Beyond	Midnight Memories	Dawn Explosion	1977
Pat Travers	Runnin' From the Future	Putting It Straight	1977
Henry Gross	Traveling Time	Plug Me Into Something	1975
Bachman Turner Overdrive	It's Over	Head On	1975
Judas Priest	Killing Machine	Killing Machine	1978
Chilliwack	Last Day of December	Rockerbox	1975
Black Sabbath	Never Say Die!	Never Say Die	1978
Joe Walsh	Welcome to the Club	So What	1975
Piper	Can't Wait	Can't Wait	1977
UFO	Lights Out	Too Hot To Handle	1977
Ram Jam	404	Ram Jam	1977
Ace Freely	I'm in Need of Love	Ace Freely	1978
The Real Kids	Do The Boob	The Real Kids	1977
Steppenwolf	The Night Time's For you	For Ladies Only	1971
Diamond Rio	Scratch My Back	Dirty Diamonds	1976
Dirty Tricks	Get Out on The Street	Hit and Run	1977
AC/DC	Soul Stripper	High Voltage	1976
Lynyrd Skynyrd	Baby Don't You Cry	Second Helping	1974
Alvin Lee	Rocket Fuel	Rocket Fuel	1978
Moxy	Cause There's Another	Moxy II	1976
Granmax	Let Me Know	A Ninth Alive	1976
Ted Nugent	Where Have You Been All My Life	Ted Nugent	1975
Detective	Dynamite	It Takes One to Know One	1978
Dirty Tricks	Last Night of Freedom	Hit & Run	1977
Yesterday & Today	Animal Woman	Yesterday & Today	1976
Thunder Mug	Big City	Ta-Daa	1975
Judas Priest	Heroes End	Strained Class	1978
Black Sabbath	The Thrill of it All	Sabotage	1975
Uriah Heap	Shady Lady	Return to Fantasy	1975
Judas Priest	Better by You, Better Than Me	Stained Class	1978

It seems probable that there were other similar programs at about this time, probably even Jeff Bender's Vinyl Underground also on WGTB. But Hard Implosion is the earliest that I've been able to document fully— down the playlists. For that reason I feel confident calling it the first known metal radio program.