Thrown together at the last minute in the dying hours of sessions for the Clash’s classic 1980 album, London Calling, “Train in Vain (Stand by Me)” was not even listed on the record’s cover. It was the Clash song that almost wasn’t, but it turned out to be the one that brought the band into the Top 30 for the first time.

A perennial critics’ favorite, London Calling is often called “the album of the ’80s.” Like many of their longtime fans, the Clash felt their 1978 album, Give ’Em Enough Rope, produced by AOR rock guru Sandy Pearlman, had made them sound too much like stadium rockers. In search of a more credible alternative, singer Joe Strummer tracked down legendary British producer Guy Stevens (Free, Mott the Hoople). The Clash weren’t just aware of Stevens’s reputation as a drunken, pill-filled studio hell-raiser — they were depending on it. The crazed moments Stevens provided — such as flooding the interior of a piano with beer to make it sound better, fighting with engineer Bill Price and passing out in a heap on top of the mixing desk — were precisely what inspired the Clash to go hell-for-leather in pursuit of new and exciting sounds.

As guitarist Mick Jones puts it, “Sure, Guy had a few drinks during the course of the session, but he wasn’t like that all the time. He was the catalyst. He was only greasing the wheels, so to speak . . . or lubricating them.”

Work on London Calling had begun in August 1979 in what Strummer called a “grimy room” in London’s Pimlico district. After a month-long American tour with soul veterans Sam & Dave, country-rocker Joe Ely and psychobilly combo the Cramps, the Clash returned to England full of ideas and completed the album at the fancier Wessex Studios in North London.

The Clash were pumping out new songs so fast — even as the album’s artwork was in production, they were writing material — that London Calling evolved into a double album.

“Train in Vain,” written in one night and recorded the next day, was initially going to be given away as a promotion with the British rock magazine New Musical Express. Only after that failed to happen did the band consider the song for inclusion on the album.

As Wessex Studios’ manager and house engineer Bill Price points out, “Train in Vain” was “the last song we finished after the artwork went to the printer. A couple of Clash Web sites describe it as a hidden track, but it wasn’t intended to be hidden. The sleeve was already printed before we tacked the song on the end of the master tape.”

The meaning of the song’s title is equally obscure. Sometimes it seems as if every little boy who once dreamed of growing up to be a train engineer became a songwriter instead. Throughout popular music, from blues to country to disco to rock, songs about trains are almost as common as songs about cars: “Chattanooga Choo Choo,” “The Midnight Special,” “Mystery Train,” “Love Train.”

With the Clash, however, things are never quite what they seem — and no train is mentioned in the song. Mick Jones, who wrote most of it, offers a prosaic explanation: “The track was like a train rhythm, and there was, once again, that feeling of being lost.”

Another curious aspect of “Train in Vain,” given the Clash’s political stance and reputation for social consciousness, is that it’s a love song, with an almost country-and-western lyric that echoes Tammy Wynette’s classic weepie “Stand by Your Man.”

If the Clash were hard-line British punks who despised America as much as their song “I’m So Bored With the U.S.A.” suggested, why did “Train in Vain” have such a made-in-the-U.S.A. feel? Strummer has admitted that despite the band’s anti-American posturing, much of its inspiration came from this side of the Atlantic Ocean. “I was drenched in blues and English R&B; as a teenager,” the singer says. “Then I went to black American R&B; with my [pre-Clash] group the 101ers. Mick had heard a lot of that stuff too, and he had this extra dimension of the glam/trash New York Dolls/Stooges scene.”

“Train in Vain” entered the U.S. charts on March 22, 1980. Although it got no higher than number 23, the cut changed how the Clash were perceived. No longer regarded as weird British punks, they were now seen as full-blooded American rockers. In effect, “Train in Vain” paved the way for the Top 10 success of the 1982 single “Rock the Casbah” (from Combat Rock) and has become a Clash standard, covered by artists as diverse as EMF, Dwight Yoakam, Annie Lennox and Third Eye Blind. Its influence crops up elsewhere, too: Listening to “Train in Vain” and Garbage’s “Stupid Girl” in succession makes clear where Garbage drummer and producer Butch Vig located “Stupid Girl” ’s distinctive drum loops.

Predictably, despite the success of “Train in Vain,” Strummer says he’s offended by those who contend that London Calling was deliberately designed to appeal to American radio listeners. “The way we made that album was about as far from America as you can get,” he gripes — but there’s no denying it provided the song that got them the airplay they needed to finally crack the United States.