Australia woke up to the arrival of AC/DC’s second album on Dec. 1, 1975. Released just months after their debut, High Voltage, T.N.T. benefitted from experiences on a rough-edged touring scene. When it reached No. 2 on the nation’s album chart, T.N.T. was a clear, explosive warning of what was to come.

Their first record had demonstrated AC/DC's potential, but it didn't offer a definitive sonic statement. The group was still feeling its way forward from the debut single, “Can I Sit Next To You, Girl,” which had been released the previous year.

By the time High Voltage was being recorded, singer Dave Evans had been replaced by Bon Scott, but brothers Angus and Malcolm Young were still alternating their guitar roles, while elder brother George – also the band's producer – was among a number of other people who received recording credits.

But T.N.T. was different. Drummer Phil Rudd and bassist Mark Evans became members of AC/DC and played on all but two of the tracks. Malcolm realized he should focus fully on rhythm guitar while Angus took all the lead parts. Their style soon turned into an unmistakably hard, solid, blues-based rock.

“There might have been one or two tracks on the first album, a few things that they were experimenting with, which probably later on they wouldn't have done anymore,” co-producer Harry Vanda later remembered. “You could say that T.N.T was the one that really pulled the identity. Like, ‘This is AC/DC, there's no doubt about it. That's who it's going to be and that's how it's going to stay.'”

Yet they still operated somewhat haphazardly. “They would force you - ‘Come on! You've got to do something a little rock ‘n’ roll! Come up with a title, we'll get a rock ‘n’ roll 12-bar behind it,’ and we sort of just got in there and did it,” Malcolm told Billboard in 2003. “We used to do a lot of writing in the studio.”

Watch AC/DC's 'High Voltage' Video

AC/DC was pressed for time, “so we would come up with a guitar riff and they'd always say, ‘We need a title. Angus, you're good for a title, give us a title.’ ‘T.N.T.!’,” Malcolm added, “and he had a little line to go with at the time, and Bon had his ideas. … We just put them on a bit of paper and went through 'em. You have to get an album done - and quick, 'cause we had no other time.”

Evans told Music Radar that he was aware the band was “really honing the classic AC/DC sound” as the members worked. "The steady, pounding rhythms, the hard-edged, twin-guitar attack, the in-your-face vocals – it was all right there,” he remembered in 2011. “It wasn't anything fancy, but it was honest. It was something everyone could relate to.”

On the subject of Malcolm and Angus Young developing their signature sound, Evans said: “I think they were very aware of how it was going to land with people. But like most great guitar duos, they were doing what came naturally. They didn't sit up at night thinking about their guitar parts or analyzing their sound – they were going on instinct.”

The biggest growth, he noted, was Malcolm locking down his rhythm licks. “As far as I'm concerned, if you've got Phil and Malcolm together, you're flying first-class. We jelled very quickly, the three of us. To be in the rhythm section of AC/DC meant being a tight unit.”

The first track written was “High Voltage” – with the title nodding toward the band's first record. Angus later told Guitar for the Practicing Musician that the song had modest beginnings: “I remember sitting home one night before going into the studio and playing around with some chords, and I suddenly thought, ‘Let's try playing A, C, D, C. Sounded good. And then I thought AC/DC ... power ... ‘High Voltage!’ I sang the chorus part to my brother in the studio and he thought it sounded great.”

Listen to AC/DC Perform 'It's a Long Way to the Top' Video

Malcolm also noted that “Live Wire” and “It’s a Long Way to the Top (If You Wanna Rock 'n' Roll)” came together “almost immediately” in the studio. “When we played live in those days, we used to jam a lot onstage because we were so short of original material,” he explained. “We used to play ‘Jumpin’ Jack Flash’ and put in 15 minutes of bullshit so we could fill up a 40-minute set.

“The riffs for ‘Live Wire’ and ‘It’s a Long Way to the Top’ came out of those jams,” he said. “Back then we never went into the studio with anything more than a riff. In fact, we thought a riff was a song. We really didn’t know any better.”

One of the album's key hooks is the bagpipes heard on “It’s a Long Way to the Top.” George Young is credited with the suggestion, after a discussion about how the open chords were ringing to the extent that a drone effect could almost already be heard. Because Scott once played in a pipe band, he was asked to do the honors, but what George Young didn’t know was that Scott was a drummer in the band.

Nevertheless, Scott had some woodwind experience, so he managed to record what was needed. The pipes – as seen in the song's video – became part of AC/DC’s live show, until Scott laid them down near the edge of a stage and the voracious audience tore them apart.

Another classic moment came with the title track. The “oi” chant that remains popular to this day came about after George heard Angus doing it as a joke, then insisted on adding it to the mix. But those elements were just icing on the cake, and it was the quality of the cake that stood out. “All of a sudden, the kid brothers were still the kid brothers,” George said later. “But my God, they knew how to play. There was no sort of ‘Do they have it or don’t they have it?’ It was obvious that they had something.”

T.N.T. was never released to the rest of the world, not even when the band put together various reissues of its back catalog. However, all but two of the LP's songs appeared on the international album High Voltage in 1976, along with two tracks from the first High Voltage record. By that time, AC/DC were well on the way to the top.

20 Greatest Comeback Albums

Becoming a successful artist is difficult. Remaining on top forever is downright impossible.

The Only Time AC/DC Was Late for a Show

More From KOOL 101.7