The opening song to one of the greatest albums of all time from the only band that mattered. The Clash’s London Calling was written by Joe Strummer and Mick Jones, and the title alludes to the BBC World Service’s station identification: “This is London calling …”, which was used during World War II, often in broadcasts to occupied countries.
According to Bobby Owsinski, the famous opening riff is actually a combination of two guitars – one is Joe Strummer’s rhythm that’s playing the Em to Cm sus, and the other is Mick Jones straight Em against it. There’s also a E pedal note that gets louder as the intro goes along. And as he notes, you can really hear the backwards guitar solo pretty well.