'When I interviewed Bono in Dublin back in January, as part of my marathon tracking of the new U2 album, No Line On the Horizon, for Sunday's Observer Music Monthly, he described it as "essentially a big fat rock album". The most dramatic exception is a track called White As Snow, the quietest, most intimate, and arguably most arresting song that U2 have ever made.

"There are a couple of songs from the point of view of an active soldier in Afghanistan," Bono told me back in June 2008, at the group's Hanover Quay studio in Dublin, during a break in recording, "and one of them, White As Snow, lasts the length of time it takes him to die".

Of all the character songs on the album, White As Snow is the most moving. Much of this is to do with its sense of quietude - not a mood one normally associates with U2. The song is almost ambient in its musical pulse, suggesting the presence of Daniel Lanois and Brian Eno, and Bono's voice sounds markedly different here, more restrained, more plaintive, the emotion suggested rather than strained for.

The song's melody is based on an old hymn, Oh Come, Oh Come, Emmanuel, that, according to The Handbook to the Lutheran Hymnal, was composed by "an unknown author, circa 1100".

The idea of a song based on the dying thoughts of a soldier initially came to Bono after he read William Golding's ambitious novel, Pincher Martin, which is told from the point of view of a British sailor who appears to have survived the torpedoing of his ship. As he approaches death, his thoughts roam back over his life, and the moral choices he made or avoided. (The novel's denouement, though, suggests that the soldier died at the moment his ship went down and that the preceding narrative recounts his soul's struggle to stay in the material world.)

After watching Sam Mendes's film, Jarhead, Bono decided the song should evoke the thoughts of a soldier dying from a roadside bomb in Afghanistan. Intriguingly, you don't really need to know the context for the song to work. It stands alone. Initially, I had assumed it was sung in the voice of a young Middle Eastern man who had been driven into exile, but there you go......'

Read the rest of Sean's blog here.